Stockholders' Equity - Schedule of Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	$ 8,085	$ 10,318	$ 7,070
Other Comprehensive Income (Loss), Net of Tax	172	(1,989)	83
Other comprehensive income (loss) attributable to McKesson	152	(1,884)	83
Ending balance	9,008	8,085	10,318
Foreign Currency Translation Adjustments, Net of Tax
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	(1,420)	168
Other comprehensive income (loss) before reclassifications	113	(1,845)	9
Amounts reclassified to earnings	0	(10)	44
Other Comprehensive Income (Loss), Net of Tax	113	(1,855)	53
Less: amounts attributable to noncontrolling and redeemable interests	16	(267)
Other comprehensive income (loss) attributable to McKesson	97	(1,588)
Ending balance	(1,323)	(1,420)	168
Unrealized Losses on Cash Flow Hedges, Net of Tax
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	(21)	(11)
Other comprehensive income (loss) before reclassifications	6	(13)	(6)
Amounts reclassified to earnings	3	3	0
Other Comprehensive Income (Loss), Net of Tax	9	(10)	(6)
Less: amounts attributable to noncontrolling and redeemable interests	0	0
Other comprehensive income (loss) attributable to McKesson	9	(10)
Ending balance	(12)	(21)	(11)
Unrealized Net Gains (Losses) and Other Components of Benefit Plans, Net of Tax
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	(272)	(160)
Other comprehensive income (loss) before reclassifications	23	(136)
Amounts reclassified to earnings	27	12
Other Comprehensive Income (Loss), Net of Tax	50	(124)	36
Less: amounts attributable to noncontrolling and redeemable interests	4	(12)
Other comprehensive income (loss) attributable to McKesson	46	(112)
Ending balance	(226)	(272)	(160)
Total Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Change, Net of Tax [Roll Forward]
Beginning balance	(1,713)	(3)	(65)
Other comprehensive income (loss) before reclassifications	142	(1,994)
Amounts reclassified to earnings	30	5
Other Comprehensive Income (Loss), Net of Tax	172	(1,989)
Less: amounts attributable to noncontrolling and redeemable interests	20	(279)
Other comprehensive income (loss) attributable to McKesson	152	(1,710)	62
Ending balance	$ (1,561)	$ (1,713)	$ (3)