Goodwill and Intangible Assets, Net - Narrative - Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018
Goodwill [Line Items]
Goodwill and asset impairment charges	$ 570	$ 0
Amortization expense of intangible assets	122	$ 121
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Estimated annual amortization expense, remainder of 2019	344
Estimated annual amortization expense, 2020	441
Estimated annual amortization expense, 2021	423
Estimated annual amortization expense, 2022	391
Estimated annual amortization expense, 2023	282
Estimated annual amortization expense, thereafter	2,377
European Pharmaceutical Solutions
Goodwill [Line Items]
Accumulated goodwill impairment losses	1,793		$ 1,299
Goodwill and asset impairment charges	570
Other
Goodwill [Line Items]
Accumulated goodwill impairment losses	448		$ 456
Goodwill and asset impairment charges	$ 0