Income From Continuing Operations Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Basic income from continuing operations per common share:
Income from continuing operations	$ 208	$ 219	$ 618	$ 598
Less: Income from continuing operations allocable to participating securities	(2)	(2)	(7)	(6)
Income from continuing operations allocable to common shares	$ 206	$ 217	$ 611	$ 592
Weighted average common shares outstanding	413	420	414	431
Basic income from continuing operations per common share (in dollars per share)	$ 0.50	$ 0.52	$ 1.48	$ 1.37
Diluted income from continuing operations per common share:
Income from continuing operations	$ 208	$ 219	$ 618	$ 598
Less: Income from continuing operations allocable to participating securities	(2)	(2)	(7)	(6)
Income from continuing operations allocable to common shares	$ 206	$ 217	$ 611	$ 592
Weighted average shares outstanding and common share equivalents:
Weighted average common shares outstanding	413	420	414	431
Weighted average effect of share-based payment awards	1	1	1	1
Denominator in calculation of diluted income per share	414	421	415	432
Diluted income from continuing operations per common share (in dollars per share)	$ 0.50	$ 0.52	$ 1.47	$ 1.37
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	2	2
Weighted average restricted stock awards considered participating securities	5	4	5	4