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				6 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Schedule of Earnings Per Share [Line Items]
Income from continuing operations	$ 491		$ 423		$ 916		$ 851
Net income attributable to noncontrolling interests	(8)		0		(16)		0
Income from continuing operations attributable to McKesson	483		423		900		851
Loss from discontinued operations, net of tax	(14)		(19)		(28)		(23)
Net income attributable to McKesson	$ 469		$ 404		$ 872		$ 828
Weighted average common shares outstanding:
Basic	232		229		231		228
Effect of dilutive securities:
Options to purchase common stock	1		2		2		1
Restricted stock units	2		2		2		3
Diluted	235		233		235		232
Earnings (Loss) Per Common Share Attributable To McKesson (Diluted)
Continuing operations	$ 2.05	[1]	$ 1.82	[1]	$ 3.83	[1]	$ 3.66	[1]
Discontinued operations	$ (0.06)	[1]	$ (0.08)	[1]	$ (0.12)	[1]	$ (0.10)	[1]
Total	$ 1.99	[1]	$ 1.74	[1]	$ 3.71	[1]	$ 3.56	[1]
Earnings (Loss) Per Common Share Attributable To McKesson (Basic)
Continuing operations	$ 2.08	[1]	$ 1.85	[1]	$ 3.89	[1]	$ 3.73	[1]
Discontinued operations	$ (0.06)	[1]	$ (0.09)	[1]	$ (0.12)	[1]	$ (0.10)	[1]
Total	$ 2.02	[1]	$ 1.76	[1]	$ 3.77	[1]	$ 3.63	[1]

[1] Certain computations may reflect rounding adjustments.