Income from Continuing Operations Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Basic income from continuing operations per common share:
Income from continuing operations	$ 899	$ 939	$ 923
Less: Income from continuing operations allocable to participating securities	(9)	(12)	(11)
Income from continuing operations allocable to common shares	890	927	912
Weighted average common shares outstanding	446	456	486
Basic income from continuing operations per common share (in dollars per share)	$ 2.00	$ 2.03	$ 1.88
Diluted income from continuing operations per common share:
Income from continuing operations	899	939	923
Less: Income from continuing operations allocable to participating securities	(9)	(12)	(11)
Income from continuing operations allocable to common shares	$ 890	$ 927	$ 912
Weighted average shares outstanding and common share equivalents:
Weighted average common shares outstanding	446	456	486
Weighted average effect of share-based payment awards	2	1	1
Denominator in calculation of diluted income per share	448	457	487
Diluted income from continuing operations per common share (in dollars per share)	$ 1.99	$ 2.03	$ 1.87
Income from continuing operations per common share, Other disclosures [Abstract]
Number of anti-dilutive restricted stock awards and options excluded from calculation	2	4	4
Weighted average restricted stock awards considered participating securities	5	5	6