Stockholders' Deficit - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (1,464)	$ (1,249)	$ (1,490)	$ (1,490)	$ (1,792)
Other comprehensive income (loss) before reclassifications	76	117		95	(173)
Amounts reclassified to earnings and other	(1)	98		(2)	852
Other comprehensive income, net of tax	75	215		93	679
Less: amounts attributable to noncontrolling interests	0	0		0	44
Other comprehensive income (loss) attributable to McKesson	75	215		93	635
Ending balance	(1,682)	(2,089)	(1,464)	(1,682)	(2,089)
Reclassified to income statement, tax		22			6
Disposed of by sale | U.K. Disposal Group (Disposal Group)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of gains from AOCI			26		26
Derivatives designated for hedge accounting | Net Investment Hedging | Currency swap
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), net investment hedge, gain (loss)	(27)	(7)		(20)	(26)
Total Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(887)	(1,114)	(905)	(905)	(1,534)
Ending balance	(812)	(899)	(887)	(812)	(899)
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(864)	(1,254)	(847)	(847)	(1,504)
Other comprehensive income (loss) before reclassifications	92	96		75	(360)
Amounts reclassified to earnings and other	0	280		0	1,027
Other comprehensive income, net of tax	92	376		75	667
Ending balance	(772)	(878)	(864)	(772)	(878)
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Less: amounts attributable to noncontrolling interests	0	0		0	41
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) attributable to McKesson	92	376		75	626
Unrealized Losses on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(9)	109	(14)	(14)	10
Other comprehensive income (loss) before reclassifications	(20)	(5)		(15)	111
Amounts reclassified to earnings and other	0	(119)		0	(136)
Other comprehensive income, net of tax	(20)	(124)		(15)	(25)
Ending balance	(29)	(15)	(9)	(29)	(15)
Other comprehensive income (loss) before reclassification, tax	7	(15)		(5)	32
Unrealized Losses on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Less: amounts attributable to noncontrolling interests	0	0		0	0
Unrealized Losses on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) attributable to McKesson	(20)	(124)		(15)	(25)
Unrealized Gains (Losses) on Cash Flow and Other Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4)	63	(36)	(36)	27
Other comprehensive income (loss) before reclassifications	5	8		37	44
Amounts reclassified to earnings and other	0	(73)		0	(73)
Other comprehensive income, net of tax	5	(65)		37	(29)
Ending balance	1	(2)	(4)	1	(2)
Unrealized Gains (Losses) on Cash Flow and Other Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Less: amounts attributable to noncontrolling interests	0	0		0	0
Unrealized Gains (Losses) on Cash Flow and Other Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) attributable to McKesson	5	(65)		37	(29)
Unrealized Losses and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(10)	(32)	(8)	(8)	(67)
Other comprehensive income (loss) before reclassifications	(1)	18		(2)	32
Amounts reclassified to earnings and other	(1)	10		(2)	34
Other comprehensive income, net of tax	(2)	28		(4)	66
Ending balance	(12)	(4)	$ (10)	(12)	(4)
Unrealized Losses and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Less: amounts attributable to noncontrolling interests	0	0		0	3
Unrealized Losses and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) attributable to McKesson	$ (2)	$ 28		$ (4)	$ 63