Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ (6,174)	$ 247	$ (5,052)	$ 54
Net income attributable to noncontrolling interests	(52)	(56)	(152)	(163)
Income (loss) from continuing operations attributable to McKesson Corporation	(6,226)	191	(5,204)	(109)
Loss from discontinued operations, net of tax	0	(5)	(1)	(12)
Net income (loss) attributable to McKesson Corporation	$ (6,226)	$ 186	$ (5,205)	$ (121)
Weighted-average common shares outstanding:
Basic (in shares)	159.5	178.7	161.2	183.1
Effect of dilutive securities:
Restricted stock units (in shares)	0.0	1.0	0.0	0.0
Diluted (in shares)	159.5	179.7	161.2	183.1
Diluted
Continuing operations (in dollars per share)	$ (39.03)	$ 1.06	$ (32.28)	$ (0.60)
Discontinued operations (in dollars per share)	0	(0.03)	(0.01)	(0.06)
Total (in dollars per share)	(39.03)	1.03	(32.29)	(0.66)
Basic
Continuing operations (in dollars per share)	(39.03)	1.06	(32.28)	(0.60)
Discontinued operations (in dollars per share)	0	(0.02)	(0.01)	(0.06)
Total (in dollars per share)	$ (39.03)	$ 1.04	$ (32.29)	$ (0.66)
Potentially dilutive securities (shares)		2.0