Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2016	Mar. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 4,970	$ 5,140
Accumulated Amortization	(1,909)	(2,119)
Net Carrying Amount	$ 3,061	3,021
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	8 years
Gross Carrying Amount	$ 2,435	2,652
Accumulated Amortization	(1,182)	(1,324)
Net Carrying Amount	$ 1,253	1,328
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	14 years
Gross Carrying Amount	$ 955	959
Accumulated Amortization	(287)	(269)
Net Carrying Amount	$ 668	690
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	24 years
Gross Carrying Amount	$ 836	857
Accumulated Amortization	(134)	(121)
Net Carrying Amount	$ 702	736
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	14 years
Gross Carrying Amount	$ 475	314
Accumulated Amortization	(99)	(96)
Net Carrying Amount	$ 376	218
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	1 year
Gross Carrying Amount	$ 66	195
Accumulated Amortization	(62)	(182)
Net Carrying Amount	$ 4	13
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	5 years
Gross Carrying Amount	$ 203	163
Accumulated Amortization	(145)	(127)
Net Carrying Amount	$ 58	$ 36