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		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Income from continuing operations	$ 649	$ 642	$ 1,647	$ 1,877
Net income attributable to noncontrolling interests	(13)	(13)	(48)	(39)
Income from continuing operations attributable to McKesson	636	629	1,599	1,838
Income (loss) from discontinued operations, net of tax	(3)	5	(117)	(11)
Net Income Attributable to McKesson Corporation	$ 633	$ 634	$ 1,482	$ 1,827
Weighted average common shares outstanding:
Basic (in shares)	221	230	224	231
Effect of dilutive securities:
Options to purchase common stock (in shares)	0	1	1	1
Restricted stock units (in shares)	1	1	1	2
Diluted (in shares)	222	232	226	234
Diluted
Continuing operations (in dollars per share)	$ 2.86	$ 2.71	$ 7.07	$ 7.86
Discontinued operations (in dollars per share)	(0.01)	0.02	(0.51)	(0.05)
Total (in dollars per share)	2.85	2.73	6.56	7.81
Basic
Continuing operations (in dollars per share)	2.89	2.74	7.14	7.95
Discontinued operations (in dollars per share)	(0.02)	0.02	(0.52)	(0.04)
Total (in dollars per share)	$ 2.87	$ 2.76	$ 6.62	$ 7.91