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
	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Income from continuing operations	$ 495	$ 483
Net income attributable to noncontrolling interests	(50)	(54)
Income from continuing operations attributable to McKesson	445	429
Loss from discontinued operations, net of tax	(1)	(6)
Net income attributable to McKesson Corporation	$ 444	$ 423
Weighted-average common shares outstanding:
Basic (in shares)	162	188
Effect of dilutive securities:
Restricted stock units (in shares)	1	1
Diluted (in shares)	163	189
Diluted
Continuing operations (in dollars per share)	$ 2.72	$ 2.27
Discontinued operations (in dollars per share)	0	(0.03)
Total (in dollars per share)	2.72	2.24
Basic
Continuing operations (in dollars per share)	2.74	2.28
Discontinued operations (in dollars per share)	0	(0.03)
Total (in dollars per share)	$ 2.74	$ 2.25
Potentially dilutive securities (shares)	3	3