Goodwill and Intangible Assets, Net - Schedule of Information Regarding Intangible Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2017	Mar. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 6,478	$ 5,758
Accumulated Amortization	(2,384)	(2,093)
Net Carrying Amount	$ 4,094	3,665
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	12 years
Gross Carrying Amount	$ 3,480	2,893
Accumulated Amortization	(1,458)	(1,295)
Net Carrying Amount	$ 2,022	1,598
Service agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	12 years
Gross Carrying Amount	$ 1,043	1,009
Accumulated Amortization	(366)	(316)
Net Carrying Amount	$ 677	693
Pharmacy licenses
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	26 years
Gross Carrying Amount	$ 630	741
Accumulated Amortization	(140)	(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	$ 914	845
Accumulated Amortization	(171)	(124)
Net Carrying Amount	$ 743	721
Technology
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	4 years
Gross Carrying Amount	$ 148	69
Accumulated Amortization	(79)	(64)
Net Carrying Amount	$ 69	5
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Average Remaining Amortization Period (years)	4 years
Gross Carrying Amount	$ 263	201
Accumulated Amortization	(170)	(144)
Net Carrying Amount	$ 93	$ 57