Income from Continuing Operations Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Basic income from continuing operations per common share:
Income from continuing operations	$ 769	$ 810	$ 887
Less: Income from continuing operations allocable to participating securities	(8)	(8)	(9)
Income from continuing operations allocable to common shares	$ 761	$ 802	$ 878
Weighted average common shares outstanding	426	439	446
Basic income from continuing operations per common share (in dollars per share)	$ 1.79	$ 1.83	$ 1.97
Diluted income from continuing operations per common share:
Income from continuing operations	$ 769	$ 810	$ 887
Less: Income from continuing operations allocable to participating securities	(8)	(8)	(9)
Income from continuing operations allocable to common shares	$ 761	$ 802	$ 878
Weighted average shares outstanding and common share equivalents:
Weighted average common shares outstanding	426	439	446
Weighted average effect of share-based payment awards	1	2	2
Denominator in calculation of diluted income per share	427	441	448
Diluted income from continuing operations per common share (in dollars per share)	$ 1.78	$ 1.82	$ 1.96
Income from continuing operations per common share, Other disclosures [Abstract]
Number of anti-dilutive restricted stock awards and options excluded from calculation	2	1	2
Weighted average restricted stock awards considered participating securities	4	4	5