Stockholders' Equity - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 5,309	$ 8,287
Other comprehensive income (loss) before reclassifications	27	64
Amounts reclassified to earnings and other	2	13
Other comprehensive income, net of tax	29	77
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	61	6
Other comprehensive income (loss) attributable to McKesson	(32)	71
Ending balance	5,653	8,068
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,780)	(1,628)
Other comprehensive income (loss) before reclassifications	96	70
Amounts reclassified to earnings and other	0	0
Other comprehensive income, net of tax	96	70
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	58	6
Other comprehensive income (loss) attributable to McKesson	38	64
Ending balance	(1,742)	(1,564)
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	138	53
Other comprehensive income (loss) before reclassifications	(63)	(26)
Amounts reclassified to earnings and other	0	0
Other comprehensive income, net of tax	(63)	(26)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	0
Other comprehensive income (loss) attributable to McKesson	(63)	(26)
Ending balance	75	27
Unrealized gains (losses) on cash flow hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	49	(37)
Other comprehensive income (loss) before reclassifications	(5)	12
Amounts reclassified to earnings and other	0	0
Other comprehensive income, net of tax	(5)	12
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	0
Other comprehensive income (loss) attributable to McKesson	(5)	12
Ending balance	44	(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	(110)	(237)
Other comprehensive income (loss) before reclassifications	(1)	8
Amounts reclassified to earnings and other	2	13
Other comprehensive income, net of tax	1	21
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	3	0
Other comprehensive income (loss) attributable to McKesson	(2)	21
Ending balance	(112)	(216)
Total Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,703)	(1,849)
Other comprehensive income (loss) attributable to McKesson	(32)	71
Ending balance	$ (1,735)	$ (1,778)