Stockholders' Equity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Basic earnings per share:
Net earnings	$ 70.7	$ 119.9	$ 114.7	$ 95.7	$ 122.5	$ 109.1	$ 131.8	$ 92.8	$ 401.0	$ 456.2	$ 406.1
Less earnings allocated to participating securities										(0.3)	(0.8)
Net earnings allocated to common shares									401.0	455.9	405.3
Weighted average number of common shares outstanding	163.3	167.2	173.0	176.3	178.1	178.2	178.3	180.3	169.9	178.7	183.1
Basic earnings per share	$ 0.43	$ 0.72	$ 0.66	$ 0.54	$ 0.69	$ 0.61	$ 0.74	$ 0.51	$ 2.36	$ 2.55	$ 2.21
Diluted earnings per share:
Net earnings	70.7	119.9	114.7	95.7	122.5	109.1	131.8	92.8	401.0	456.2	406.1
Less earnings allocated to participating securities										(0.3)	(0.8)
Net earnings allocated to common shares									$ 401.0	$ 455.9	$ 405.3
Weighted average number of common shares outstanding	163.3	167.2	173.0	176.3	178.1	178.2	178.3	180.3	169.9	178.7	183.1
Incremental shares from assumed conversions of share-based awards									2.9	3.7	3.7
Adjusted weighted average number of common shares outstanding	165.6	169.5	176.0	180.6	182.3	182.3	181.4	183.8	172.8	182.4	186.8
Diluted earnings per share	$ 0.43	$ 0.71	$ 0.65	$ 0.53	$ 0.67	$ 0.60	$ 0.73	$ 0.50	$ 2.32	$ 2.50	$ 2.17