Noncontrolling Interests and Redeemable Noncontrolling Interests - Schedule of Changes in Noncontrolling Interests and Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Jul. 31, 2014	Apr. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance			$ 84
Net income attributable to noncontrolling interests			52	$ 67	$ (5)
Ending balance			84	84
Noncontrolling interests
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		$ 1,796	84	1,796
Net income attributable to noncontrolling interests			8	5
Other comprehensive loss			0	(174)
Purchase of noncontrolling interests				(60)
Reclassification from Total Equity to Redeemable Noncontrolling Interests (5)				(1,500)
Reclassification of guaranteed dividends and recurring compensation to other accrued liabilities			0	0
Other			(8)	17
Ending balance			84	84	1,796
Celesio | Noncontrolling interests
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Purchase of noncontrolling interests	$ (25)	(35)
Celesio | Redeemable Noncontrolling Interests
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance		$ 0	1,386	0
Net income attributable to noncontrolling interests			44	62
Other comprehensive loss			20	(105)
Purchase of noncontrolling interests				(9)
Reclassification from Total Equity to Redeemable Noncontrolling Interests (5)				1,500
Reclassification of guaranteed dividends and recurring compensation to other accrued liabilities			(44)	(62)
Other			0	0
Ending balance			$ 1,406	$ 1,386	$ 0