Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Income from continuing operations	$ 310	$ 627	$ 846	$ 1,122
Net income attributable to noncontrolling interests	(43)	(50)	(90)	(100)
Income from continuing operations attributable to McKesson Corporation	267	577	756	1,022
Loss from discontinued operations, net of tax	0	0	(3)	(1)
Net income attributable to McKesson Corporation	$ 267	$ 577	$ 753	$ 1,021
Weighted-average common shares outstanding:
Basic (in shares)	154.1	162.0	155.1	162.0
Effect of dilutive securities:
Diluted (in shares)	155.8	163.2	156.9	163.2
Diluted
Continuing operations (in dollars per share)	$ 1.71	$ 3.54	$ 4.82	$ 6.26
Discontinued operations (in dollars per share)	0	0	(0.02)	0
Total (in dollars per share)	1.71	3.54	4.80	6.26
Basic
Continuing operations (in dollars per share)	1.73	3.56	4.87	6.31
Discontinued operations (in dollars per share)	0	0	(0.02)	(0.01)
Total (in dollars per share)	$ 1.73	$ 3.56	$ 4.85	$ 6.30
Potentially dilutive securities (shares)	1.0	2.0	1.0	2.0
Stock options
Effect of dilutive securities:
Restricted stock units (in shares)	0.2	0.0	0.2	0.0
Restricted stock units
Effect of dilutive securities:
Restricted stock units (in shares)	1.5	1.2	1.6	1.2