Income From Continuing Operations Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic income from continuing operations per common share:
Income from continuing operations	$ 212	$ 172	$ 410	$ 379
Less: Income from continuing operations allocable to participating securities	(3)	(2)	(5)	(4)
Income from continuing operations allocable to common shares	$ 209	$ 170	$ 405	$ 375
Weighted average common shares outstanding	414	436	414	436
Basic income from continuing operations per common share (in dollars per share)	$ 0.50	$ 0.39	$ 0.98	$ 0.86
Diluted income from continuing operations per common share:
Income from continuing operations	$ 212	$ 172	$ 410	$ 379
Less: Income from continuing operations allocable to participating securities	(3)	(2)	(5)	(4)
Income from continuing operations allocable to common shares	$ 209	$ 170	$ 405	$ 375
Weighted average shares outstanding and common share equivalents:
Weighted average common shares outstanding	414	436	414	436
Weighted average effect of share-based payment awards	1	1	1	1
Denominator in calculation of diluted income per share	415	437	415	437
Diluted income from continuing operations per common share (in dollars per share)	$ 0.50	$ 0.39	$ 0.98	$ 0.86
Income from continuing operations per common share, Other disclosures [Abstract]
Number of anti-dilutive restricted stock awards and options excluded from the calculation	1	2	1	2
Weighted average restricted stock awards considered participating securities	5	5	5	4