Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Mar. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,488	$ 5,758
Accumulated Amortization	(2,250)	(2,093)
Net Carrying Amount	$ 4,238	3,665
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	12 years
Gross Carrying Amount	$ 3,411	2,893
Accumulated Amortization	(1,392)	(1,295)
Net Carrying Amount	$ 2,019	1,598
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	13 years
Gross Carrying Amount	$ 1,023	1,009
Accumulated Amortization	(332)	(316)
Net Carrying Amount	$ 691	693
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	25 years
Gross Carrying Amount	$ 772	741
Accumulated Amortization	(164)	(150)
Net Carrying Amount	$ 608	591
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	15 years
Gross Carrying Amount	$ 870	845
Accumulated Amortization	(136)	(124)
Net Carrying Amount	$ 734	721
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	5 years
Gross Carrying Amount	$ 151	69
Accumulated Amortization	(71)	(64)
Net Carrying Amount	$ 80	5
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	5 years
Gross Carrying Amount	$ 261	201
Accumulated Amortization	(155)	(144)
Net Carrying Amount	$ 106	$ 57