Stockholders' Equity (Deficit) - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (87)	$ 6,090	$ 175	$ 5,309
Other comprehensive income (loss) before reclassifications		50		90
Amounts reclassified to income statement		69		71
Other comprehensive income (loss), net of tax	8	119	(4)	161
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests		25		(39)
Other comprehensive income (loss) attributable to McKesson	8	94	(7)	200
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			8	3
Ending balance	(787)	(277)	(787)	(277)
Total Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,665)	(1,597)	(1,480)	(1,703)
Other comprehensive income (loss) before reclassifications	9		(24)
Amounts reclassified to income statement	(1)		20
Other comprehensive income (loss), net of tax	8		(4)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	(2)		1
Other comprehensive income (loss) attributable to McKesson	10	94	(5)	200
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			(170)
Ending balance	(1,655)	(1,503)	(1,655)	(1,503)
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,557)	(1,512)	(1,361)	(1,780)
Other comprehensive income (loss) before reclassifications	0	156	(47)	363
Amounts reclassified to income statement	0	47	18	47
Other comprehensive income (loss), net of tax	0	203	(29)	410
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	(2)	20	7	(41)
Other comprehensive income (loss) attributable to McKesson	2	183	(36)	451
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			(158)
Ending balance	(1,555)	(1,329)	(1,555)	(1,329)
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(25)	6	(36)	138
Other comprehensive income (loss) before reclassifications	16	(96)	21	(229)
Amounts reclassified to income statement	0	0	0	0
Other comprehensive income (loss), net of tax	16	(96)	21	(229)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	0	(6)	(1)
Other comprehensive income (loss) attributable to McKesson	16	(96)	27	(228)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			0
Ending balance	(9)	(90)	(9)	(90)
Other comprehensive income (loss) before reclassifications, tax	(5)	33	(10)	80
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	23	(84)	34	(201)
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	(2)	(45)	3	(108)
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	21	25	13	49
Other comprehensive income (loss) before reclassifications	(6)	(12)	(3)	(36)
Amounts reclassified to income statement	0	0	5	0
Other comprehensive income (loss), net of tax	(6)	(12)	2	(36)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	0	0	0
Other comprehensive income (loss) attributable to McKesson	(6)	(12)	2	(36)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			0
Ending balance	15	13	15	13
Unrealized Net Gains (Losses) and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(104)	(116)	(96)	(110)
Other comprehensive income (loss) before reclassifications	(1)	2	5	(8)
Amounts reclassified to income statement	(1)	22	(3)	24
Other comprehensive income (loss), net of tax	(2)	24	2	16
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	5	0	3
Other comprehensive income (loss) attributable to McKesson	(2)	19	2	13
Exercise of put right by noncontrolling shareholders of McKesson Europe AG			(12)
Ending balance	$ (106)	$ (97)	$ (106)	$ (97)