Earnings Per Common Share (Basic and Diluted Earnings per Common Share) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Jun. 30, 2014		Jun. 30, 2013
Schedule of Earnings Per Share [Line Items]
Income from continuing operations	$ 425		$ 428
Net income attributable to noncontrolling interests	(8)		0
Income from continuing operations attributable to McKesson	417		428
Loss from discontinued operations, net of tax	(14)		(4)
Net income attributable to McKesson	$ 403		$ 424
Weighted average common shares outstanding:
Basic	231		227
Effect of dilutive securities:
Options to purchase common stock	2		2
Restricted stock units	2		3
Diluted	235		232
Earnings (Loss) Per Common Share Attributable To McKesson (Diluted)
Continuing operations	$ 1.78	[1]	$ 1.84	[1]
Discontinued operations	$ (0.06)	[1]	$ (0.01)	[1]
Total	$ 1.72	[1]	$ 1.83	[1]
Earnings (Loss) Per Common Share Attributable To McKesson (Basic)
Continuing operations	$ 1.81	[1]	$ 1.88	[1]
Discontinued operations	$ (0.06)	[1]	$ (0.02)	[1]
Total	$ 1.75	[1]	$ 1.86	[1]

[1] Certain computations may reflect rounding adjustments.