Stockholders' Equity - Schedule of Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	$ 175	$ 5,309	$ 8,287
Other comprehensive income, net of tax	115	170	149
Other comprehensive income attributable to McKesson	112	223	146
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	8	3
Ending balance	(1,792)	175	5,309
Derivatives used in Net Investment Hedge, Increase (Decrease), Gross of Tax	73	(118)	39
Actuarial gains (losses) from pension plans	5	0	(127)
Net Investment Hedging | Derivatives designated for hedge accounting
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Derivatives used in Net Investment Hedge, Increase (Decrease), Gross of Tax	(4)	(119)	76
Foreign Currency Translation Adjustments, Net of Tax
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	(1,361)	(1,780)	(1,628)
Other comprehensive income (loss) before reclassifications	(51)	312	(151)
Amount reclassified to earnings and other	71	47	0
Other comprehensive income, net of tax	20	359	(151)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	5	(60)	1
Other comprehensive income attributable to McKesson	15	419	(152)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	(158)
Ending balance	(1,504)	(1,361)	(1,780)
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	(36)	138	53
Other comprehensive income (loss) before reclassifications	41	(175)	85
Amount reclassified to earnings and other	(1)	0	0
Other comprehensive income, net of tax	40	(175)	85
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	(6)	(1)	0
Other comprehensive income attributable to McKesson	46	(174)	85
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	0
Ending balance	10	(36)	138
Unrealized gain (loss) on net investment hedges, tax	(23)	62	(30)
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	13	49	(37)
Other comprehensive income (loss) before reclassifications	18	(36)	86
Amount reclassified to earnings and other	(4)	0	0
Other comprehensive income, net of tax	14	(36)	86
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	0	0
Other comprehensive income attributable to McKesson	14	(36)	86
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	0
Ending balance	27	13	49
Unrealized Gains (Losses) and Other Components of Benefit Plans, Net of Tax
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	(96)	(110)	(237)
Other comprehensive income (loss) before reclassifications	31	(2)	33
Amount reclassified to earnings and other	10	24	96
Other comprehensive income, net of tax	41	22	129
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	8	2
Other comprehensive income attributable to McKesson	41	14	127
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	(12)
Ending balance	(67)	(96)	(110)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	(1,480)	(1,703)	(1,849)
Other comprehensive income (loss) before reclassifications	39	99	53
Amount reclassified to earnings and other	76	71	96
Other comprehensive income, net of tax	115	170	149
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	(1)	(53)	3
Other comprehensive income attributable to McKesson	116	223	146
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	(170)
Ending balance	$ (1,534)	$ (1,480)	(1,703)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Reclassification from AOCI, Current Period, Tax			$ 33