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, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Income (Loss) from continuing operations	$ 483	$ (81)
Net income attributable to noncontrolling interests	(54)	(58)
Income (Loss) from continuing operations attributable to McKesson	429	(139)
Income (Loss) from discontinued operations, net of tax	(6)	1
Net Income (Loss) Attributable to McKesson Corporation	$ 423	$ (138)
Weighted average common shares outstanding:
Basic (in shares)	188	202
Effect of dilutive securities:
Restricted stock units (in shares)	1	0
Diluted (in shares)	189	202
Diluted
Continuing operations (in dollars per share)	$ 2.27	$ (0.69)
Discontinued operations (in dollars per share)	(0.03)	0.01
Total (in dollars per share)	2.24	(0.68)
Basic
Continuing operations (in dollars per share)	2.28	(0.69)
Discontinued operations (in dollars per share)	(0.03)	0.01
Total (in dollars per share)	$ 2.25	$ (0.68)