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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Income from continuing operations	$ 552	$ 56	$ 471	$ 419
Net income attributable to noncontrolling interests	(54)	(55)	(112)	(111)
Income from continuing operations attributable to McKesson	498	1	359	308
Income from discontinued operations, net of tax	1	0	2	2
Net Income Attributable to McKesson Corporation	$ 499	$ 1	$ 361	$ 310
Weighted average common shares outstanding:
Basic (in shares)	198	209	200	210
Effect of dilutive securities:
Options to purchase common stock (in shares)	0	0	0	0
Restricted stock units (in shares)	1	1	1	1
Diluted (in shares)	199	210	201	211
Diluted
Continuing operations (in dollars per share)	$ 2.51	$ 0.01	$ 1.79	$ 1.46
Discontinued operations (in dollars per share)	0.00	0.00	0.01	0.01
Total (in dollars per share)	2.51	0.01	1.80	1.47
Basic
Continuing operations (in dollars per share)	2.52	0.01	1.80	1.47
Discontinued operations (in dollars per share)	0.00	0.00	0.01	0.01
Total (in dollars per share)	$ 2.52	$ 0.01	$ 1.81	$ 1.48