Redeemable Noncontrolling Interests and Noncontrolling Interests - Narrative (Details) shares in Millions	3 Months Ended			6 Months Ended
	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($) shares	Apr. 12, 2021 € / shares	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 19, 2018 € / shares	Dec. 31, 2014 € / shares
Noncontrolling Interest [Line Items]
Put right redemption price per share (in euros per share) | € / shares						€ 22.99				€ 23.50	€ 22.99
Put right value, interest rate spread (as a percent)											5.00%
Increase in put amount (in Euros per share) | € / shares										€ 0.51
Payments for purchase shares of McKesson Europe				$ 1,031,000,000	$ 49,000,000
Associated increase in Company's ownership interest on its equity				8,000,000	3,000,000
Reclassification of McKesson Europe redeemable noncontrolling interests				(287,000,000)
Carrying value of redeemable noncontrolling interests	$ 0			0			$ 1,271,000,000
Net income attributable to noncontrolling interests	43,000,000		$ 50,000,000	90,000,000	100,000,000
Redeemable Noncontrolling Interests
Noncontrolling Interest [Line Items]
Net income attributable to noncontrolling interests	0		10,000,000	8,000,000	21,000,000
Decrease in noncontrolling interest				983,000,000	49,000,000
Reclassification of McKesson Europe redeemable noncontrolling interests				287,000,000
Carrying value of redeemable noncontrolling interests	0	$ 7,000,000	1,265,000,000	0	1,265,000,000		1,271,000,000	$ 1,414,000,000	$ 1,402,000,000
Additional Paid-in Capital
Noncontrolling Interest [Line Items]
Associated increase in Company's ownership interest on its equity				178,000,000	3,000,000
Noncontrolling Interests
Noncontrolling Interest [Line Items]
Reclassification of McKesson Europe redeemable noncontrolling interests				(287,000,000)
Net income attributable to noncontrolling interests	$ 43,000,000		40,000,000	82,000,000	79,000,000
McKesson Europe Subsidiary
Noncontrolling Interest [Line Items]
Annual recurring dividend (in euro per share) | € / shares						€ 0.83					€ 0.83
McKesson Europe Subsidiary
Noncontrolling Interest [Line Items]
Net income attributable to noncontrolling interests		$ 8,000,000	10,000,000		21,000,000
Payments for purchase shares of McKesson Europe				$ 1,000,000,000	$ 49,000,000
Shares purchased (shares) | shares				34.5	1.8
Carrying value of redeemable noncontrolling interests							1,300,000,000
Maximum redemption value of redeemable noncontrolling interest							$ 1,200,000,000
Ownership percentage (as a percent)	95.00%			95.00%			78.00%
Vantage and ClarusOne Sourcing Services LLC
Noncontrolling Interest [Line Items]
Net income attributable to noncontrolling interests	$ 43,000,000		$ 40,000,000	$ 82,000,000	$ 79,000,000