Stockholders' Equity - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (1,739)		$ (1,561)
Other comprehensive income (loss) before reclassifications	(115)		(382)
Amounts reclassified to earnings and other	1		24
Other Comprehensive Income (Loss), Net of Tax	(114)	$ (230)	(358)	$ 93
Less: amounts attributable to redeemable noncontrolling interests	1		(65)
Other comprehensive income (loss) attributable to McKesson	(115)		(293)
Ending balance	(1,854)		(1,854)
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(1,511)		(1,323)
Other comprehensive income (loss) before reclassifications	(109)		(384)
Amounts reclassified to earnings and other	0		20
Other Comprehensive Income (Loss), Net of Tax	(109)		(364)
Less: amounts attributable to redeemable noncontrolling interests	1		(66)
Other comprehensive income (loss) attributable to McKesson	(110)		(298)
Ending balance	(1,621)		(1,621)
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(12)		(12)
Other comprehensive income (loss) before reclassifications	(6)		(6)
Amounts reclassified to earnings and other	0		0
Other Comprehensive Income (Loss), Net of Tax	(6)		(6)
Less: amounts attributable to redeemable noncontrolling interests	0		0
Other comprehensive income (loss) attributable to McKesson	(6)		(6)
Ending balance	(18)		(18)
Unrealized Net Gains (Losses) and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(216)		(226)
Other comprehensive income (loss) before reclassifications	0		8
Amounts reclassified to earnings and other	1		4
Other Comprehensive Income (Loss), Net of Tax	1		12
Less: amounts attributable to redeemable noncontrolling interests	0		1
Other comprehensive income (loss) attributable to McKesson	1		11
Ending balance	$ (215)		$ (215)