Earnings Per Common Share (Details) (USD $) In Millions, except Per Share data	3 Months Ended				6 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Income from continuing operations	$ 296		$ 255		$ 582		$ 553
Discontinued operation - gain on sale, net of tax			72				72
Net Income	$ 296		$ 327		$ 582		$ 625
Weighted average common shares outstanding:
Basic	246		258		247		262
Effect of dilutive securities:
Diluted	250		262		252		267
Basic
Continuing operations	$ 1.20	[1]	$ 0.99	[1]	$ 2.35	[1]	$ 2.11	[1]
Discontinued operation - gain on sale			$ 0.28	[1]			$ 0.28	[1]
Total	$ 1.20	[1]	$ 1.27	[1]	$ 2.35	[1]	$ 2.39	[1]
Diluted
Continuing operations	$ 1.18	[1]	$ 0.97	[1]	$ 2.31	[1]	$ 2.07	[1]
Discontinued operation - gain on sale			$ 0.28	[1]			$ 0.27	[1]
Total	$ 1.18	[1]	$ 1.25	[1]	$ 2.31	[1]	$ 2.34	[1]
Earnings Per Common Share
Potentially dilutive shares excluded from diluted earnings per share	1		2		4		6
Options To Purchase Common Stock [Member]
Effect of dilutive securities:
Dilutive securities	1		2		2		3
Restricted Stock Units [Member]
Effect of dilutive securities:
Dilutive securities	3		2		3		2

[1] Certain computations may reflect rounding adjustments.