Stockholders' Equity - Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance			$ (1,713)
Other Comprehensive Income (Loss), Net of Tax	$ (230)	$ (671)	93	$ (573)
Balance at June 30, 2015	(1,644)		(1,644)
Parent Company
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	(1,434)		(1,713)
Other comprehensive income (loss) before reclassifications	(240)		82
Amounts reclassified to earnings and other	10		11
Other Comprehensive Income (Loss), Net of Tax	(230)		93
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	(20)		24
Other comprehensive income (loss) attributable to McKesson	(210)		69
Balance at June 30, 2015	(1,644)		(1,644)
Foreign Currency Translation Adjustments, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	(1,123)		(1,420)
Other comprehensive income (loss) before reclassifications	(243)		104
Amounts reclassified to earnings and other	0		0
Other Comprehensive Income (Loss), Net of Tax	(243)		104
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	(20)		30
Other comprehensive income (loss) attributable to McKesson	(223)		74
Balance at June 30, 2015	(1,346)		(1,346)
Unrealized Gains (Losses) on Cash Flow Hedges, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	(17)		(21)
Other comprehensive income (loss) before reclassifications	2		6
Amounts reclassified to earnings and other	0		0
Other Comprehensive Income (Loss), Net of Tax	2		6
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0		0
Other comprehensive income (loss) attributable to McKesson	2		6
Balance at June 30, 2015	(15)		(15)
Unrealized Net Gains (Losses) and Other Components of Benefit Plans, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	(294)		(272)
Other comprehensive income (loss) before reclassifications	1		(28)
Amounts reclassified to earnings and other	10		11
Other Comprehensive Income (Loss), Net of Tax	11		(17)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0		(6)
Other comprehensive income (loss) attributable to McKesson	11		(11)
Balance at June 30, 2015	$ (283)		$ (283)