Stockholders' Equity (Deficit) - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 175	$ 5,309
Other comprehensive income (loss) before reclassifications	12	27
Amounts reclassified to earnings and other	14	2
Other comprehensive income (loss), net of tax	26	29
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	3	61
Other comprehensive income (loss) attributable to McKesson	23	(32)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	8	3
Ending balance	(45)	5,653
Total Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,480)	(1,703)
Other comprehensive income (loss) attributable to McKesson	23	(32)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	(170)
Ending balance	(1,627)	(1,735)
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,361)	(1,780)
Other comprehensive income (loss) before reclassifications	34	96
Amounts reclassified to earnings and other	17	0
Other comprehensive income (loss), net of tax	51	96
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	9	58
Other comprehensive income (loss) attributable to McKesson	42	38
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	(158)
Ending balance	(1,477)	(1,742)
Unrealized Losses on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(36)	138
Other comprehensive income (loss) before reclassifications	(27)	(63)
Amounts reclassified to earnings and other	0	0
Other comprehensive income (loss), net of tax	(27)	(63)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	(6)	0
Other comprehensive income (loss) attributable to McKesson	(21)	(63)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	0
Ending balance	(57)	75
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	13	49
Other comprehensive income (loss) before reclassifications	0	(5)
Amounts reclassified to earnings and other	0	0
Other comprehensive income (loss), net of tax	0	(5)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	0
Other comprehensive income (loss) attributable to McKesson	0	(5)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	0
Ending balance	13	44
Unrealized Net Gains (Losses) and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(96)	(110)
Other comprehensive income (loss) before reclassifications	5	(1)
Amounts reclassified to earnings and other	(3)	2
Other comprehensive income (loss), net of tax	2	1
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	3
Other comprehensive income (loss) attributable to McKesson	2	(2)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	(12)
Ending balance	$ (106)	$ (112)