Stockholders' Deficit - Schedule of Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (1,381,000,000)	$ (1,240,000,000)	$ (1,599,000,000)	$ (1,490,000,000)
Other comprehensive income (loss) before reclassifications	24,000,000	(38,000,000)	(8,000,000)	19,000,000
Amounts reclassified to earnings and other	(1,000,000)	(1,000,000)	(1,000,000)	(1,000,000)
Other comprehensive income (loss), net of tax	23,000,000	(39,000,000)	(9,000,000)	18,000,000
Less: amounts attributable to noncontrolling interests	0	0	0	0
Other comprehensive income (loss) attributable to McKesson	23,000,000	(39,000,000)	(9,000,000)	18,000,000
Ending balance	(2,642,000,000)	(1,464,000,000)	(2,642,000,000)	(1,464,000,000)
Other comprehensive income (loss), cash flows hedge, gain (loss) reclassification, before tax	0	0	0	0
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)	(20,000,000)	27,000,000	(13,000,000)	7,000,000
Derivatives designated for hedge accounting | Cash Flow Hedges | Currency swap
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), cash flows hedge, gain (loss) reclassification, before tax	(14,000,000)	33,000,000	(14,000,000)	27,000,000
Derivatives designated for hedge accounting | Cash Flow Hedges | Fixed interest rate swaps
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), cash flows hedge, gain (loss) reclassification, before tax	0	0	0	16,000,000
Derivatives designated for hedge accounting | Cash Flow Hedges | Foreign currency forwards
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), cash flows hedge, gain (loss) reclassification, before tax	2,000,000	0	2,000,000	0
Total Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(913,000,000)	(848,000,000)	(881,000,000)	(905,000,000)
Ending balance	(890,000,000)	(887,000,000)	(890,000,000)	(887,000,000)
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(892,000,000)	(780,000,000)	(856,000,000)	(847,000,000)
Other comprehensive income (loss) before reclassifications	49,000,000	(84,000,000)	13,000,000	(17,000,000)
Amounts reclassified to earnings and other	0	0	0	0
Other comprehensive income (loss), net of tax	49,000,000	(84,000,000)	13,000,000	(17,000,000)
Ending balance	(843,000,000)	(864,000,000)	(843,000,000)	(864,000,000)
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	0
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) attributable to McKesson	49,000,000	(84,000,000)	13,000,000	(17,000,000)
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(7,000,000)	(29,000,000)	(12,000,000)	(14,000,000)
Other comprehensive income (loss) before reclassifications	(15,000,000)	20,000,000	(10,000,000)	5,000,000
Amounts reclassified to earnings and other	0	0	0	0
Other comprehensive income (loss), net of tax	(15,000,000)	20,000,000	(10,000,000)	5,000,000
Ending balance	(22,000,000)	(9,000,000)	(22,000,000)	(9,000,000)
Other comprehensive income (loss) before reclassification, tax	(5,000,000)	7,000,000	(3,000,000)	(2,000,000)
Unrealized Gains (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 Gains (Losses) on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) attributable to McKesson	(15,000,000)	20,000,000	(10,000,000)	5,000,000
Unrealized Gains (Losses) on Cash Flow and Other Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	3,000,000	(29,000,000)	3,000,000	(36,000,000)
Other comprehensive income (loss) before reclassifications	(9,000,000)	25,000,000	(9,000,000)	32,000,000
Amounts reclassified to earnings and other	0	0	0	0
Other comprehensive income (loss), net of tax	(9,000,000)	25,000,000	(9,000,000)	32,000,000
Ending balance	(6,000,000)	(4,000,000)	(6,000,000)	(4,000,000)
Other comprehensive income (loss) before reclassification, tax	(3,000,000)	8,000,000	(3,000,000)	11,000,000
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	(9,000,000)	25,000,000	(9,000,000)	32,000,000
Unrealized Gains (Losses) and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(17,000,000)	(10,000,000)	(16,000,000)	(8,000,000)
Other comprehensive income (loss) before reclassifications	(1,000,000)	1,000,000	(2,000,000)	(1,000,000)
Amounts reclassified to earnings and other	(1,000,000)	(1,000,000)	(1,000,000)	(1,000,000)
Other comprehensive income (loss), net of tax	(2,000,000)	0	(3,000,000)	(2,000,000)
Ending balance	(19,000,000)	(10,000,000)	(19,000,000)	(10,000,000)
Unrealized Gains (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	0
Unrealized Gains (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	$ (2,000,000)	$ 0	$ (3,000,000)	$ (2,000,000)