Stockholders' Equity - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 11,273
Other comprehensive income (loss) before reclassifications	320
Amounts reclassified to earnings and other	1
Other Comprehensive Income (Loss), Net of Tax	321	$ (244)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	116
Other comprehensive income (loss) attributable to McKesson	205
Ending balance	11,513
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,873)
Other comprehensive income (loss) before reclassifications	382	(275)
Amounts reclassified to earnings and other	0	20
Other Comprehensive Income (Loss), Net of Tax	382	(255)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	115
Other comprehensive income (loss) attributable to McKesson	267
Ending balance	(1,606)
Unrealized Losses on Net Investment Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(8)
Other comprehensive income (loss) before reclassifications	(70)	0
Amounts reclassified to earnings and other	0	0
Other Comprehensive Income (Loss), Net of Tax	(70)	0
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0
Other comprehensive income (loss) attributable to McKesson	(70)
Ending balance	(78)
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(31)
Other comprehensive income (loss) before reclassifications	14
Amounts reclassified to earnings and other	0
Other Comprehensive Income (Loss), Net of Tax	14	$ 0
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0
Other comprehensive income (loss) attributable to McKesson	14
Ending balance	(17)
Unrealized Net Gains (Losses) and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(229)
Other comprehensive income (loss) before reclassifications	(6)
Amounts reclassified to earnings and other	1
Other Comprehensive Income (Loss), Net of Tax	(5)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	1
Other comprehensive income (loss) attributable to McKesson	(6)
Ending balance	(235)
Total Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(2,141)
Ending balance	$ (1,936)