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Goodwill and Intangible Assets, Net - Goodwill Narrative (Details) $ in Millions	6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2021 segment	Mar. 31, 2021 USD ($) segment	Mar. 31, 2022 USD ($) segment	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)
Goodwill [Line Items]
Number of reportable segments \| segment	4	4	4
Goodwill impairment charge			$ 0	$ 69	$ 2
Goodwill		$ 9,493	9,451	9,493	9,360
International
Goodwill [Line Items]
Goodwill impairment charge				69
Goodwill		1,535	1,533	1,535	$ 1,443
Accumulated goodwill impairment loss		3,600	$ 700	3,600
International \| Europe
Goodwill [Line Items]
Goodwill		$ 0		0
Retail Pharmacy Reporting Unit [Member] \| International
Goodwill [Line Items]
Goodwill impairment charge				$ 69