Consolidated Statements of Stockholders' Equity (USD $) In Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance at May. 31, 2010	$ 1,402.0	$ 3.6	$ 499.7	$ 856.3	$ 42.4
Beginning balance, shares at May. 31, 2010		361.5
Net income	515.3			515.3
Unrealized gains/(losses) on securities, net of tax	(4.9)				(4.9)
Cash dividends declared	(448.8)			(448.8)
Stock-based compensation	25.0		25.0
Stock-based award transactions, Shares		0.6
Stock-based award transactions, Value	7.6		10.9	(3.3)
Ending balance at May. 31, 2011	1,496.2	3.6	535.6	919.5	37.5
Ending balance, Shares at May. 31, 2011		362.1
Net income	548.0			548.0
Unrealized gains/(losses) on securities, net of tax	0.2				0.2
Cash dividends declared	(460.5)			(460.5)
Stock-based compensation	23.1		23.1
Stock-based award transactions, Shares		0.5
Stock-based award transactions, Value	(2.5)		2.4	(4.9)
Ending balance at May. 31, 2012	1,604.5	3.6	561.1	1,002.1	37.7
Ending balance, Shares at May. 31, 2012	362.6	362.6
Net income	569.0			569.0
Unrealized gains/(losses) on securities, net of tax	(15.7)				(15.7)
Cash dividends declared	(476.7)			(476.7)
Stock-based compensation	22.9		22.9
Stock-based award transactions, Shares		2.8
Stock-based award transactions, Value	69.7	0.1	75.5	(5.9)
Ending balance at May. 31, 2013	$ 1,773.7	$ 3.7	$ 659.5	$ 1,088.5	$ 22.0
Ending balance, Shares at May. 31, 2013	365.4	365.4