Quarterly Financial Data (Quarterly Financial Data) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
3 Months Ended | 12 Months Ended | |||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
May 31, 2017 |
Feb. 28, 2017 |
Nov. 30, 2016 |
Aug. 31, 2016 |
May 31, 2016 |
Feb. 29, 2016 |
Nov. 30, 2015 |
Aug. 31, 2015 |
May 31, 2017 |
May 31, 2016 |
May 31, 2015 |
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| Quarterly Financial Data [Abstract] | |||||||||||||||||||||||||
| Service revenue | $ 784.6 | $ 782.6 | $ 760.0 | $ 773.5 | $ 741.6 | $ 740.7 | $ 711.3 | $ 712.2 | $ 3,100.7 | $ 2,905.8 | $ 2,697.5 | ||||||||||||||
| Interest on funds held for clients | 14.0 | 13.2 | 11.4 | 12.0 | 12.3 | 11.9 | 11.1 | 10.8 | 50.6 | 46.1 | 42.1 | ||||||||||||||
| Total revenue | 798.6 | 795.8 | 771.4 | 785.5 | 753.9 | 752.6 | 722.4 | 723.0 | 3,151.3 | 2,951.9 | 2,739.6 | ||||||||||||||
| Operating income | 298.9 | 306.6 | 311.1 | 323.0 | 276.3 | 280.0 | 294.2 | 296.1 | 1,239.6 | 1,146.6 | 1,053.6 | ||||||||||||||
| Investment income/(loss), net | 1.6 | 1.2 | 0.9 | 1.5 | (0.2) | 1.7 | 1.6 | 1.4 | 5.2 | 4.5 | 6.4 | ||||||||||||||
| Income before income taxes | 300.5 | 307.8 | 312.0 | 324.5 | 276.1 | 281.7 | 295.8 | 297.5 | 1,244.8 | 1,151.1 | 1,060.0 | ||||||||||||||
| Income taxes | 105.2 | 105.3 | 109.9 | 107.1 | 98.0 | 101.3 | 106.6 | 88.4 | 427.5 | 394.3 | 385.1 | ||||||||||||||
| Net income | $ 195.3 | $ 202.5 | $ 202.1 | $ 217.4 | $ 178.1 | $ 180.4 | $ 189.2 | $ 209.1 | $ 817.3 | $ 756.8 | $ 674.9 | ||||||||||||||
| Basic earnings per share | $ 0.54 | [1] | $ 0.56 | [1] | $ 0.56 | [1] | $ 0.60 | [1] | $ 0.49 | [1] | $ 0.50 | [1] | $ 0.52 | [1] | $ 0.58 | [1] | $ 2.27 | [1] | $ 2.10 | [1] | $ 1.86 | ||||
| Diluted earnings per share | $ 0.54 | [1] | $ 0.56 | [1] | $ 0.56 | [1] | $ 0.60 | [1] | $ 0.49 | [1] | $ 0.50 | [1] | $ 0.52 | [1] | $ 0.58 | [1] | $ 2.25 | [1] | $ 2.09 | [1] | $ 1.85 | ||||
| Weighted-average common shares outstanding | 359.3 | 359.0 | 360.2 | 361.0 | 360.3 | 360.5 | 360.7 | 361.1 | 359.8 | 360.7 | 362.9 | ||||||||||||||
| Weighted-average common shares outstanding, assuming dilution | 362.1 | 361.8 | 362.6 | 364.1 | 362.6 | 362.2 | 362.3 | 362.8 | 362.6 | 362.5 | 364.6 | ||||||||||||||
| Cash dividends per common share | $ 0.46 | $ 0.46 | $ 0.46 | $ 0.46 | $ 0.42 | $ 0.42 | $ 0.42 | $ 0.42 | $ 1.84 | $ 1.68 | $ 1.52 | ||||||||||||||
| Total net realized gains | $ 0.1 | [2] | $ 0.1 | [2] | $ 0.1 | [2] | $ 0.1 | [2] | $ 0.3 | ||||||||||||||||
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- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Aggregate dividends paid during the period for each share of common stock outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The net amount of nonoperating interest income (expense). No definition available.
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- Definition Amount of operating interest income, including, but not limited to, amortization and accretion of premiums and discounts on securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period). Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The net result for the period of deducting operating expenses from operating revenues. No definition available.
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- References No definition available.
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- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Aggregate revenue during the period from services rendered in the normal course of business, after deducting allowances and discounts. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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