Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,682	$ 6,664
Accumulated Amortization	(3,082)	(2,975)
Net Carrying Amount	$ 3,600	3,689
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	12 years
Gross Carrying Amount	$ 3,831	3,818
Accumulated Amortization	(1,871)	(1,801)
Net Carrying Amount	$ 1,960	2,017
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	11 years
Gross Carrying Amount	$ 1,022	1,017
Accumulated Amortization	(447)	(430)
Net Carrying Amount	$ 575	587
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	26 years
Gross Carrying Amount	$ 513	513
Accumulated Amortization	(210)	(209)
Net Carrying Amount	$ 303	304
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	13 years
Gross Carrying Amount	$ 893	887
Accumulated Amortization	(244)	(232)
Net Carrying Amount	$ 649	655
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	4 years
Gross Carrying Amount	$ 141	141
Accumulated Amortization	(98)	(94)
Net Carrying Amount	$ 43	47
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	5 years
Gross Carrying Amount	$ 282	288
Accumulated Amortization	(212)	(209)
Net Carrying Amount	$ 70	$ 79