CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (4,340)	$ 1,120	$ 255
Other comprehensive income (loss), net of tax
Foreign currency translation adjustments	184	(66)	(190)
Unrealized gains (losses) on cash flow hedges	(36)	86	24
Changes in retirement-related benefit plans	22	129	(32)
Other comprehensive income (loss), net of tax	170	149	(198)
Comprehensive income (loss)	(4,170)	1,269	57
Comprehensive income attributable to noncontrolling interests	(146)	(223)	(155)
Comprehensive income (loss) attributable to McKesson Corporation	$ (4,316)	$ 1,046	$ (98)