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		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Income from continuing operations	$ 325	$ 636	$ 998	$ 1,235
Net income attributable to noncontrolling interests	(17)	(13)	(35)	(26)
Income from continuing operations attributable to McKesson	308	623	963	1,209
Loss from discontinued operations, net of tax	(1)	(6)	(114)	(16)
Net Income Attributable to McKesson Corporation	$ 307	$ 617	$ 849	$ 1,193
Weighted average common shares outstanding:
Basic (in shares)	226	232	226	232
Effect of dilutive securities:
Options to purchase common stock (in shares)	1	2	1	1
Restricted stock units (in shares)	1	1	1	2
Diluted (in shares)	228	235	228	235
Diluted
Continuing operations (in dollars per share)	$ 1.35	$ 2.65	$ 4.22	$ 5.15
Discontinued operations (in dollars per share)	(0.01)	(0.02)	(0.50)	(0.07)
Total (in dollars per share)	1.34	2.63	3.72	5.08
Basic
Continuing operations (in dollars per share)	1.36	2.68	4.27	5.21
Discontinued operations (in dollars per share)	0.00	(0.02)	(0.51)	(0.06)
Total (in dollars per share)	$ 1.36	$ 2.66	$ 3.76	$ 5.15