Income From Continuing Operations Per Common Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic income from continuing operations per common share:
Income from continuing operations	$ 235	$ 231	$ 447	$ 561
Less: Income from continuing operations allocable to participating securities	(2)	(2)	(4)	(6)
Income from continuing operations allocable to common shares	233	229	443	555
Weighted average common shares outstanding	440	448	440	449
Basic income from continuing operations per common share (in dollars per share)	$ 0.53	$ 0.51	$ 1.01	$ 1.24
Diluted income from continuing operations per common share:
Income from continuing operations	235	231	447	561
Less: Income from continuing operations allocable to participating securities	(2)	(2)	(4)	(6)
Income from continuing operations allocable to common shares	$ 233	$ 229	$ 443	$ 555
Weighted average shares outstanding and common share equivalents:
Weighted average common shares outstanding	440	448	440	449
Weighted average effect of share-based payment awards	1	2	1	1
Denominator in calculation of diluted income per share	441	450	441	450
Diluted income from continuing operations per common share (in dollars per share)	$ 0.53	$ 0.51	$ 1.00	$ 1.23
Income from continuing operations per common share, Other disclosures [Abstract]
Number of anti-dilutive restricted stock awards and options excluded from the calculation	2	2	2	2
Weighted average restricted stock awards considered participating securities	5	5	4	5