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Redeemable Noncontrolling Interests and Noncontrolling Interests - Narrative (Details) shares in Millions, $ in Millions		12 Months Ended
	Sep. 19, 2018 € / shares	Mar. 31, 2021 USD ($) shares	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Apr. 12, 2021 € / shares	Mar. 31, 2021 € / shares	Mar. 31, 2018 USD ($)
Noncontrolling Interest [Line Items]
Annual increase in interest (percent)		5.00%
Exercise of put right by noncontrolling shareholders of McKesson Europe		$ 3
Carrying amount of redeemable noncontrolling interest		1,271	$ 1,402
Noncontrolling interests		196	217
Net income attributable to noncontrolling interests		199	220	$ 221
Redeemable Noncontrolling Interests
Noncontrolling Interest [Line Items]
Net income attributable to noncontrolling interests		43	42	45
Exercise of put right by noncontrolling shareholders of McKesson Europe		(49)
Carrying amount of redeemable noncontrolling interest		1,271	1,402	1,393			$ 1,459
Additional Paid-in Capital
Noncontrolling Interest [Line Items]
Exercise of put right by noncontrolling shareholders of McKesson Europe		3
McKesson Europe
Noncontrolling Interest [Line Items]
Net income attributable to noncontrolling interests		43	42	45
Put right (in euro per share) \| € / shares	€ 23.50					€ 22.99
Payments to purchase shares of McKesson Europe		$ 49
Shares purchased (shares) \| shares		1.8
Maximum redemption value		$ 1,200	$ 1,200
Percentage of outstanding common shares		78.00%	77.00%
Put Right increase (euros per share) \| € / shares	€ 0.51
Vantage and ClarusOne Sourcing Services LLC
Noncontrolling Interest [Line Items]
Net income attributable to noncontrolling interests		$ 156	$ 178	$ 176
McKesson Europe
Noncontrolling Interest [Line Items]
Annual recurring compensation (in euro per share) \| € / shares						€ 0.83
Subsequent Event \| McKesson Europe
Noncontrolling Interest [Line Items]
Put right (in euro per share) \| € / shares					€ 22.99
Subsequent Event \| McKesson Europe
Noncontrolling Interest [Line Items]
Annual recurring compensation (in euro per share) \| € / shares					€ 0.83