Earnings Per Common Share - Basic and Diluted Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Income from continuing operations	$ 636	$ 491	$ 1,235	$ 910
Net income attributable to noncontrolling interests	(13)	(8)	(26)	(16)
Income from continuing operations attributable to McKesson	623	483	1,209	894
Loss from discontinued operations, net of tax	(6)	(14)	(16)	(22)
Net Income Attributable to McKesson Corporation	$ 617	$ 469	$ 1,193	$ 872
Weighted average common shares outstanding:
Basic (in shares)	232	232	232	231
Effect of dilutive securities:
Options to purchase common stock (in shares)	2	1	1	2
Restricted stock units (in shares)	1	2	2	2
Diluted (in shares)	235	235	235	235
Diluted
Continuing operations (in dollars per share)	$ 2.65	$ 2.05	$ 5.15	$ 3.80
Discontinued operations (in dollars per share)	(0.02)	(0.06)	(0.07)	(0.09)
Total (in dollars per share)	2.63	1.99	5.08	3.71
Basic
Continuing operations (in dollars per share)	2.68	2.08	5.21	3.86
Discontinued operations (in dollars per share)	(0.02)	(0.06)	(0.06)	(0.09)
Total (in dollars per share)	$ 2.66	$ 2.02	$ 5.15	$ 3.77