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Related Party Balances and Transactions (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
McKesson Foundation
Related Party Transaction [Line Items]
Contributions made	$ 20
Investee
Related Party Transaction [Line Items]
Revenue from related parties		$ 178	$ 141	$ 137
Investee \| U.S. Pharmaceutical and Specialty Solutions [Member]
Related Party Transaction [Line Items]
Revenue from related parties		$ 111	$ 60	34
Other accrued liabilities \| California Foundation
Related Party Transaction [Line Items]
Pledge payable balance				$ 100