Stockholders' Equity - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 8,287	$ 10,057
Other comprehensive income (loss) before reclassifications	64	(121)
Amounts reclassified to earnings	13	0
Other Comprehensive Income (Loss), Net of Tax	77	(121)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	6	(37)
Other comprehensive income (loss) attributable to McKesson	71	(84)
Ending balance	8,068	9,647
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,628)	(1,258)
Other comprehensive income (loss) before reclassifications	70	(273)
Amounts reclassified to earnings	0	0
Other Comprehensive Income (Loss), Net of Tax	70	(273)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	6	(39)
Other comprehensive income (loss) attributable to McKesson	64	(234)
Ending balance	(1,564)	(1,492)
Unrealized Gains (Losses) on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	53	(188)
Other comprehensive income (loss) before reclassifications	(26)	144
Amounts reclassified to earnings	0	0
Other Comprehensive Income (Loss), Net of Tax	(26)	144
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	0
Other comprehensive income (loss) attributable to McKesson	(26)	144
Ending balance	27	(44)
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(37)	(61)
Other comprehensive income (loss) before reclassifications	12	0
Amounts reclassified to earnings	0	0
Other Comprehensive Income (Loss), Net of Tax	12	0
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	0
Other comprehensive income (loss) attributable to McKesson	12	0
Ending balance	(25)	(61)
Unrealized Net Gains (Losses) and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(237)	(210)
Other comprehensive income (loss) before reclassifications	8	8
Amounts reclassified to earnings	13	0
Other Comprehensive Income (Loss), Net of Tax	21	8
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0	2
Other comprehensive income (loss) attributable to McKesson	21	6
Ending balance	(216)	(204)
Total Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,849)	(1,717)
Other comprehensive income (loss) attributable to McKesson	71	(84)
Ending balance	$ (1,778)	$ (1,801)