Goodwill and Intangible Assets, Net - Goodwill Impairment Inputs (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Goodwill [Line Items]
Goodwill impairment charge				$ 69	$ 2	$ 1,797
International
Goodwill [Line Items]
Goodwill impairment charge				69	$ 2	$ 1,776
International | Pharmaceutical Distribution
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)			8.00%
Goodwill impairment, terminal growth rate (percent)			1.25%
Goodwill impairment charge			$ 238
International | Retail Pharmacy
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)	10.00%		8.50%
Goodwill impairment, terminal growth rate (percent)	1.25%		1.25%
Goodwill impairment charge	$ 465		$ 251	$ 69
International | Pharmaceutical Distribution
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)			8.00%
Goodwill impairment, terminal growth rate (percent)			1.25%
Goodwill impairment charge			$ 81
International | Pharmaceutical Distribution
Goodwill [Line Items]
Goodwill impairment, discount rate (percent)	9.00%
Goodwill impairment, terminal growth rate (percent)	1.25%
Goodwill impairment charge	$ 741
International | Rexall Health
Goodwill [Line Items]
Goodwill impairment charge		$ 21