Goodwill and Intangible Assets, Net - Narrative - Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Goodwill [Line Items]
Amortization expense of intangible assets	$ 122	$ 123	$ 365	$ 370
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Estimated annual amortization expense, remainder of 2019	112		112
Estimated annual amortization expense, 2020	429		429
Estimated annual amortization expense, 2021	412		412
Estimated annual amortization expense, 2022	379		379
Estimated annual amortization expense, 2023	274		274
Estimated annual amortization expense, thereafter	2,314		2,314
European Pharmaceutical Solutions
Goodwill [Line Items]
Accumulated goodwill impairment losses	1,736		1,736		$ 1,299
Other
Goodwill [Line Items]
Accumulated goodwill impairment losses	$ 452		$ 452		$ 456