Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Income (loss) from continuing operations	$ 39	$ (6,174)	$ 885	$ (5,052)
Net income attributable to noncontrolling interests	46	52	136	152
Income (loss) from continuing operations attributable to McKesson Corporation	(7)	(6,226)	749	(5,204)
Loss from discontinued operations, net of tax	0	0	(3)	(1)
Net income (loss) attributable to McKesson Corporation	$ (7)	$ (6,226)	$ 746	$ (5,205)
Weighted-average common shares outstanding:
Basic (in shares)	151.6	159.5	154.0	161.2
Effect of dilutive securities:
Diluted (in shares)	151.6	159.5	155.8	161.2
Diluted
Continuing operations (in usd per share)	$ (0.04)	$ (39.03)	$ 4.81	$ (32.28)
Discontinued operations (in usd per share)	0	0	(0.02)	(0.01)
Total (in dollars per share)	(0.04)	(39.03)	4.79	(32.29)
Basic
Continuing operations (in usd per share)	(0.04)	(39.03)	4.87	(32.28)
Discontinued operations (in usd per share)	0	0	(0.02)	(0.01)
Total (in dollars per share)	$ (0.04)	$ (39.03)	$ 4.85	$ (32.29)
Potentially dilutive securities (shares)			1.0
Stock options
Effect of dilutive securities:
Restricted stock units (in shares)	0.0	0.0	0.2	0.0
Restricted stock units
Effect of dilutive securities:
Restricted stock units (in shares)	0.0	0.0	1.6	0.0