Earnings Per Common Share - Schedule of Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Income from continuing operations	$ 465	$ 642	$ 636	$ 599	$ 411	$ 521	$ 491	$ 419	$ 2,342	$ 1,842	$ 1,414
Net (income) loss attributable to noncontrolling interests									(52)	(67)	5
Income from continuing operations attributable to McKesson									2,290	1,775	1,419
Loss from discontinued operations, net of tax	(21)	5	(6)	(10)	(267)	(10)	(14)	(8)	(32)	(299)	(156)
Net Income Attributable to McKesson Corporation	$ 431	$ 634	$ 617	$ 576	$ 132	$ 472	$ 469	$ 403	$ 2,258	$ 1,476	$ 1,263
Weighted average common shares outstanding:
Basic (in shares)									230	232	229
Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Diluted (in shares)									233	235	233
Diluted
Continuing operations (in dollars per share)	$ 1.97	$ 2.71	$ 2.65	$ 2.50	$ 1.69	$ 2.04	$ 2.05	$ 1.76	$ 9.84	$ 7.54	$ 6.08
Discontinued operations (in dollars per share)	(0.09)	0.02	(0.02)	(0.05)	(1.13)	(0.04)	(0.06)	(0.04)	(0.14)	(1.27)	(0.67)
Total (in dollars per share)	1.88	2.73	2.63	2.45	0.56	2.00	1.99	1.72	9.70	6.27	5.41
Basic
Continuing operations (in dollars per share)	1.99	2.74	2.68	2.53	1.72	2.07	2.08	1.79	9.96	7.66	6.19
Discontinued operations (in dollars per share)	(0.09)	0.02	(0.02)	(0.04)	(1.15)	(0.04)	(0.06)	(0.04)	(0.14)	(1.29)	(0.68)
Total (in dollars per share)	$ 1.90	$ 2.76	$ 2.66	$ 2.49	$ 0.57	$ 2.03	$ 2.02	$ 1.75	$ 9.82	$ 6.37	$ 5.51
Stock Option
Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Effect of dilutive securities (in shares)									1	1	1
Restricted stock units
Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Effect of dilutive securities (in shares)									2	2	3