Basic and Diluted Earnings Per Share (Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended																12 Months Ended
	May 31, 2019		Feb. 28, 2019		Nov. 30, 2018		Aug. 31, 2018		May 31, 2018	[1]	Feb. 28, 2018	[1]	Nov. 30, 2017	[1]	Aug. 31, 2017	[1]	May 31, 2019		May 31, 2018		May 31, 2017	[4]
Basic earnings per share:
Net income	$ 230.4		$ 324.6		$ 235.8		$ 243.6		$ 217.7		$ 367.2		$ 198.8		$ 210.4		$ 1,034.4		$ 994.1	[1],[2],[3]	$ 826.3	[2],[3]
Weighted-average common shares outstanding	359.4		359.2		359.1		359.1		359.0		359.2		359.1		358.9		359.2		359.0	[1],[2]	359.8	[2]
Basic earnings per share	$ 0.64	[5]	$ 0.90	[5]	$ 0.66	[5]	$ 0.68	[5]	$ 0.61	[5]	$ 1.02	[5]	$ 0.55	[5]	$ 0.59	[5]	$ 2.88	[5]	$ 2.77	[1],[2],[5]	$ 2.30	[2]
Diluted earnings per share:
Net income	$ 230.4		$ 324.6		$ 235.8		$ 243.6		$ 217.7		$ 367.2		$ 198.8		$ 210.4		$ 1,034.4		$ 994.1	[1],[2],[3]	$ 826.3	[2],[3]
Weighted-average common shares outstanding	359.4		359.2		359.1		359.1		359.0		359.2		359.1		358.9		359.2		359.0	[1],[2]	359.8	[2]
Dilutive effect of common share equivalents																	2.6		2.5	[4]	2.8
Weighted-average common shares outstanding, assuming dilution	362.5		361.6		361.5		361.5		361.5		362.0		361.4		361.3		361.8		361.5	[1],[2]	362.6	[2]
Diluted earnings per share	$ 0.64	[5]	$ 0.90	[5]	$ 0.65	[5]	$ 0.67	[5]	$ 0.60	[5]	$ 1.01	[5]	$ 0.55	[5]	$ 0.58	[5]	$ 2.86	[5]	$ 2.75	[1],[2],[5]	$ 2.28	[2],[6]
Weighted-average anti-dilutive common share equivalents																	0.4		0.7	[4]	0.7

[1] Amounts have been adjusted to reflect the adoption of ASC Topic 606.

[2] Amounts have been adjusted to reflect the adoption of Accounting Standards Codification ("ASC") Topic 606, "Revenue from Contracts with Customers" ("ASC Topic 606").

[3] Amounts have been adjusted to reflect the adoption of Accounting Standards Update ("ASU") No. 2016-18, "Statement of Cash Flows (Topic 230): Restricted Cash (a consensus of the FASB Emerging Issues Task Force)."

[4] Amounts have been adjusted to reflect the adoption of ASC Topic 606.

[5] Each quarter is a discrete period and the sum of the four quarters' basic and diluted earnings per share amounts may not equal the full year amount.

[6] Diluted earnings per share amounts may not add across by +/- $0.01 due to rounding.