Earnings Per Common Share - Schedule of Computation for Basic and Diluted Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ 627	$ (676)	$ 1,122	$ (193)
Net income attributable to noncontrolling interests	(50)	(53)	(100)	(107)
Income (loss) from continuing operations attributable to McKesson	577	(729)	1,022	(300)
Loss from discontinued operations, net of tax	0	(1)	(1)	(7)
Net income (loss) attributable to McKesson Corporation	$ 577	$ (730)	$ 1,021	$ (307)
Weighted-average common shares outstanding:
Basic (in shares)	162	183	162	185
Effect of dilutive securities:
Restricted stock units (in shares)	1	0	1	0
Diluted (in shares)	163	183	163	185
Diluted
Continuing operations (in dollars per share)	$ 3.54	$ (3.99)	$ 6.26	$ (1.62)
Discontinued operations (in dollars per share)	0	0	0	(0.03)
Total (in dollars per share)	3.54	(3.99)	6.26	(1.65)
Basic
Continuing operations (in dollars per share)	3.56	(3.99)	6.31	(1.62)
Discontinued operations (in dollars per share)	0	0	(0.01)	(0.03)
Total (in dollars per share)	$ 3.56	$ (3.99)	$ 6.30	$ (1.65)
Potentially dilutive securities (shares)	2		2