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, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Income from continuing operations	$ 363	$ 673
Net income attributable to noncontrolling interests	(56)	(18)
Income from continuing operations attributable to McKesson	307	655
Income (loss) from discontinued operations, net of tax	2	(113)
Net Income Attributable to McKesson Corporation	$ 309	$ 542
Weighted average common shares outstanding:
Basic (in shares)	211	225
Effect of dilutive securities:
Options to purchase common stock (in shares)	1	1
Restricted stock units (in shares)	1	2
Diluted (in shares)	213	228
Diluted
Continuing operations (in dollars per share)	$ 1.44	$ 2.88
Discontinued operations (in dollars per share)	0.01	(0.50)
Total (in dollars per share)	1.45	2.38
Basic
Continuing operations (in dollars per share)	1.46	2.91
Discontinued operations (in dollars per share)	0.00	(0.50)
Total (in dollars per share)	$ 1.46	$ 2.41