Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2017	Mar. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,636	$ 5,758
Accumulated Amortization	(2,430)	(2,093)
Net Carrying Amount	$ 4,206	3,665
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	12 years
Gross Carrying Amount	$ 3,472	2,893
Accumulated Amortization	(1,378)	(1,295)
Net Carrying Amount	$ 2,094	1,598
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	12 years
Gross Carrying Amount	$ 1,041	1,009
Accumulated Amortization	(351)	(316)
Net Carrying Amount	$ 690	693
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	26 years
Gross Carrying Amount	$ 798	741
Accumulated Amortization	(308)	(150)
Net Carrying Amount	$ 490	591
Trademarks and trade names
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	14 years
Gross Carrying Amount	$ 910	845
Accumulated Amortization	(156)	(124)
Net Carrying Amount	$ 754	721
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	5 years
Gross Carrying Amount	$ 151	69
Accumulated Amortization	(74)	(64)
Net Carrying Amount	$ 77	5
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	5 years
Gross Carrying Amount	$ 264	201
Accumulated Amortization	(163)	(144)
Net Carrying Amount	$ 101	$ 57