Stockholders' Equity (Changes in Accumulated Other Comprehensive Income (Loss) by Component) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	$ (1,713)
Other Comprehensive Income (Loss), Net of Tax	323	$ 98
Balance at June 30, 2015	(1,434)
Parent Company
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	(1,713)
Other comprehensive income (loss) before reclassifications	322
Amounts reclassified to earnings and other	1
Other Comprehensive Income (Loss), Net of Tax	323
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	44
Other comprehensive income (loss) attributable to McKesson	279
Balance at June 30, 2015	(1,434)
Foreign currency translation adjustments, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	(1,420)
Other comprehensive income (loss) before reclassifications	347
Amounts reclassified to earnings and other	0
Other Comprehensive Income (Loss), Net of Tax	347
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	50
Other comprehensive income (loss) attributable to McKesson	297
Balance at June 30, 2015	(1,123)
Unrealized losses on cash flow hedges, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	(21)
Other comprehensive income (loss) before reclassifications	4
Amounts reclassified to earnings and other	0
Other Comprehensive Income (Loss), Net of Tax	4
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	0
Other comprehensive income (loss) attributable to McKesson	4
Balance at June 30, 2015	(17)
Unrealized net loss and other components of benefit plans, net of tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance	(272)
Other comprehensive income (loss) before reclassifications	(29)
Amounts reclassified to earnings and other	1
Other Comprehensive Income (Loss), Net of Tax	(28)
Less: amounts attributable to noncontrolling and redeemable noncontrolling interests	(6)
Other comprehensive income (loss) attributable to McKesson	(22)
Balance at June 30, 2015	$ (294)