Stockholders' Equity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010
Basic earnings per share:
Net earnings	$ 119.9	$ 109.1	$ 330.3	$ 333.7
Less earnings allocated to participating securities		(0.1)		(0.3)
Net earnings allocated to common shares	119.9	109.0	330.3	333.4
Weighted average number of common shares outstanding	167.2	178.2	172.0	178.7
Basic earnings per share	$ 0.72	$ 0.61	$ 1.92	$ 1.87
Diluted earnings per share:
Net earnings	119.9	109.1	330.3	333.7
Less earnings allocated to participating securities		(0.1)		(0.3)
Net earnings allocated to common shares	$ 119.9	$ 109.0	$ 330.3	$ 333.4
Weighted average number of common shares outstanding	167.2	178.2	172.0	178.7
Incremental shares from assumed conversions of share-based awards	2.3	4.1	3.2	3.5
Adjusted weighted average number of common shares outstanding	169.5	182.3	175.2	182.2
Diluted earnings per share	$ 0.71	$ 0.60	$ 1.88	$ 1.83