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, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share [Abstract]
Income from continuing operations	$ 3,630	$ 649	$ 325	$ 673	$ 465	$ 642	$ 636	$ 599	$ 5,277	$ 2,342	$ 1,842
Net income attributable to noncontrolling interests									(83)	(52)	(67)
Income from continuing operations attributable to McKesson									5,194	2,290	1,775
Loss from discontinued operations, net of tax	(7)	(3)	(1)	(113)	(21)	5	(6)	(10)	(124)	(32)	(299)
Net Income Attributable to McKesson Corporation	$ 3,588	$ 633	$ 307	$ 542	$ 431	$ 634	$ 617	$ 576	$ 5,070	$ 2,258	$ 1,476
Weighted average common shares outstanding:
Basic (in shares)									221	230	232
Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Diluted (in shares)									223	233	235
Diluted
Continuing operations (in dollars per share)	$ 16.79	$ 2.86	$ 1.35	$ 2.88	$ 1.97	$ 2.71	$ 2.65	$ 2.50	$ 23.28	$ 9.84	$ 7.54
Discontinued operations (in dollars per share)	(0.03)	(0.01)	(0.01)	(0.50)	(0.09)	0.02	(0.02)	(0.05)	(0.55)	(0.14)	(1.27)
Total (in dollars per share)	16.76	2.85	1.34	2.38	1.88	2.73	2.63	2.45	22.73	9.70	6.27
Basic
Continuing operations (in dollars per share)	16.95	2.89	1.36	2.91	1.99	2.74	2.68	2.53	23.50	9.96	7.66
Discontinued operations (in dollars per share)	(0.03)	(0.02)	0.00	(0.50)	(0.09)	0.02	(0.02)	(0.04)	(0.55)	(0.14)	(1.29)
Total (in dollars per share)	$ 16.92	$ 2.87	$ 1.36	$ 2.41	$ 1.90	$ 2.76	$ 2.66	$ 2.49	$ 22.95	$ 9.82	$ 6.37
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)									1	2	2

No definition available.

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- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 55
-Paragraph 52
-URI http://asc.fasb.org/extlink&oid=65016374&loc=d3e4984-109258

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64863997&loc=d3e1252-109256

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(21))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(23))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882