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, 2016	Jun. 30, 2015
Earnings Per Share [Abstract]
Income from continuing operations	$ 673	$ 599
Net income attributable to noncontrolling interests	(18)	(13)
Income from continuing operations attributable to McKesson	655	586
Loss from discontinued operations, net of tax	(113)	(10)
Net Income Attributable to McKesson Corporation	$ 542	$ 576
Weighted average common shares outstanding:
Basic (in shares)	225	232
Effect of dilutive securities:
Options to purchase common stock (in shares)	1	1
Restricted stock units (in shares)	2	2
Diluted (in shares)	228	235
Diluted
Continuing operations (in dollars per share)	$ 2.88	$ 2.50
Discontinued operations (in dollars per share)	(0.50)	(0.05)
Total (in dollars per share)	2.38	2.45
Basic
Continuing operations (in dollars per share)	2.91	2.53
Discontinued operations (in dollars per share)	(0.50)	(0.04)
Total (in dollars per share)	$ 2.41	$ 2.49