Income from Continuing Operations Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Basic income from continuing operations per common share:
Income from continuing operations	$ 938	$ 823	$ 759
Income from continuing operations allocable to common shares	927	812	751
Weighted-average common shares outstanding	486	506	515
Basic income from continuing operations per common share	$ 1.91	$ 1.60	$ 1.46
Diluted income from continuing operations per common share:
Income from continuing operations	938	823	759
Add: Interest expense associated with Convertible Senior Notes, net of tax	0	0	21
Income from continuing operations allocable to common shares	927	812	772
Weighted average shares outstanding and common share equivalents:
Weighted-average common shares outstanding	486	506	515
Weighted average shares outstanding upon conversion of Convertible Senior Notes	0	0	16
Weighted average effect of share-based payment awards	1	1	2
Denominator in calculation of diluted income per share	487	507	533
Diluted income from continuing operations per common share	$ 1.90	$ 1.60	$ 1.45
Income Per Common Share (Textual) [Abstract]
Number of anti-dilutive restricted stock awards and options excluded from the calculation	4	6	6
Weighted average restricted stock awards considered participating securities	6	6	5
Basic [Member]
Reconciliation of earnings per common share [Line Items]
Less: Income from continuing operations allocable to participating securities	(11)	(11)	(8)
Diluted [Member]
Reconciliation of earnings per common share [Line Items]
Less: Income from continuing operations allocable to participating securities	$ (11)	$ (11)	$ (8)