Quarterly Financial Information (Unaudited) - Schedule Of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 48,713	$ 50,130	$ 49,957	$ 49,733	$ 46,678	$ 47,899	$ 48,761	$ 47,546	$ 198,533	$ 190,884	$ 179,045
Gross profit	2,796	2,812	2,756	2,907	2,852	2,872	2,844	2,848	11,271	11,416	11,411
Income (loss) after income taxes:
Continuing operations	3,630	649	325	673	465	642	636	599	5,277	2,342	1,842
Discontinued operations	(7)	(3)	(1)	(113)	(21)	5	(6)	(10)	(124)	(32)	(299)
Net Income	3,623	646	324	560	444	647	630	589	5,153	2,310	1,543
Net income attributable to McKesson	$ 3,588	$ 633	$ 307	$ 542	$ 431	$ 634	$ 617	$ 576	$ 5,070	$ 2,258	$ 1,476
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