Redeemable Noncontrolling Interests - Effect of Changes in Ownership Interest (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Noncontrolling Interest [Abstract]
Net income attributable to McKesson Corporation	$ 617	$ 469	$ 1,193	$ 872
Decrease in McKesson Corporation’s paid-in capital for purchase of noncontrolling shares	0	(6)	0	(3)
Net transfers to noncontrolling and redeemable noncontrolling interests	0	(6)	0	(3)
Changes from net income attributable to McKesson Corporation and transfers to noncontrolling and redeemable noncontrolling interests	$ 617	$ 463	$ 1,193	$ 869