Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2016	Mar. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 5,354	$ 5,140
Accumulated Amortization	(2,211)	(2,119)
Net Carrying Amount	$ 3,143	3,021
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	8 years
Gross Carrying Amount	$ 2,769	2,652
Accumulated Amortization	(1,383)	(1,324)
Net Carrying Amount	$ 1,386	1,328
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	14 years
Gross Carrying Amount	$ 959	959
Accumulated Amortization	(283)	(269)
Net Carrying Amount	$ 676	690
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	25 years
Gross Carrying Amount	$ 806	857
Accumulated Amortization	(127)	(121)
Net Carrying Amount	$ 679	736
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	14 years
Gross Carrying Amount	$ 391	314
Accumulated Amortization	(99)	(96)
Net Carrying Amount	$ 292	218
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	2 years
Gross Carrying Amount	$ 195	195
Accumulated Amortization	(185)	(182)
Net Carrying Amount	$ 10	13
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	4 years
Gross Carrying Amount	$ 234	163
Accumulated Amortization	(134)	(127)
Net Carrying Amount	$ 100	$ 36