Stockholders' Equity (Deficit) - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (45)	$ 5,653	$ 175	$ 5,309
Other comprehensive income (loss) before reclassifications	(45)	13	(33)	40
Amounts reclassified to income statement	7	0	21	2
Other comprehensive income (loss), net of tax	(38)	13	(12)	42
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	(125)	3	(64)
Other comprehensive income (loss) attributable to McKesson	(38)	138	(15)	106
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			8	3
Ending balance	(87)	6,090	(87)	6,090
Total Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,627)	(1,735)	(1,480)	(1,703)
Other comprehensive income (loss) attributable to McKesson	(38)	138	(15)	106
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			(170)
Ending balance	(1,665)	(1,597)	(1,665)	(1,597)
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,477)	(1,742)	(1,361)	(1,780)
Other comprehensive income (loss) before reclassifications	(81)	111	(47)	207
Amounts reclassified to income statement	1	0	18	0
Other comprehensive income (loss), net of tax	(80)	111	(29)	207
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	(119)	9	(61)
Other comprehensive income (loss) attributable to McKesson	(80)	230	(38)	268
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			(158)
Ending balance	(1,557)	(1,512)	(1,557)	(1,512)
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(57)	75	(36)	138
Other comprehensive income (loss) before reclassifications	32	(70)	5	(133)
Amounts reclassified to income statement	0	0	0	0
Other comprehensive income (loss), net of tax	32	(70)	5	(133)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	(1)	(6)	(1)
Other comprehensive income (loss) attributable to McKesson	32	(69)	11	(132)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			0
Ending balance	(25)	6	(25)	6
Unrealized gains (losses) on net investment hedges arising during period, tax	11	(25)	5	(47)
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax | Foreign Exchange Contract
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications	33	(83)	11	(117)
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax | Cross Currency Contract
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications	10	(12)	5	(63)
Unrealized Gains on Cash Flow Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	13	44	13	49
Other comprehensive income (loss) before reclassifications	3	(19)	3	(24)
Amounts reclassified to income statement	5	0	5	0
Other comprehensive income (loss), net of tax	8	(19)	8	(24)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	0	0	0
Other comprehensive income (loss) attributable to McKesson	8	(19)	8	(24)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			0
Ending balance	21	25	21	25
Unrealized Net Gains (Losses) and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(106)	(112)	(96)	(110)
Other comprehensive income (loss) before reclassifications	1	(9)	6	(10)
Amounts reclassified to income statement	1	0	(2)	2
Other comprehensive income (loss), net of tax	2	(9)	4	(8)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	(5)	0	(2)
Other comprehensive income (loss) attributable to McKesson	2	(4)	4	(6)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			(12)
Ending balance	$ (104)	$ (116)	$ (104)	$ (116)