Quarterly Financial Information (Unaudited) - Schedule Of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 51,628	$ 53,617	$ 52,061	$ 51,051	$ 48,713	$ 50,130	$ 49,957	$ 49,733	$ 208,357	$ 198,533	$ 190,884
Gross profit	3,075	2,715	2,834	2,560	2,796	2,812	2,756	2,907	11,184	11,271	11,416
Income (loss) after income taxes:
Continuing operations	(1,087)	960	56	363	3,630	649	325	673	292	5,277	2,342
Discontinued operations	2	1	0	2	(7)	(3)	(1)	(113)	5	(124)	(32)
Net Income	(1,085)	961	56	365	3,623	646	324	560	297	5,153	2,310
Net income (loss) attributable to McKesson	$ (1,146)	$ 903	$ 1	$ 309	$ 3,588	$ 633	$ 307	$ 542	$ 67	$ 5,070	$ 2,258
Diluted
Continuing operations (in dollars per share)	$ (5.58)	$ 4.32	$ 0.01	$ 1.44	$ 16.79	$ 2.86	$ 1.35	$ 2.88	$ 0.30	$ 23.28	$ 9.84
Discontinued operations (in dollars per share)	0.00	0.01	0.00	0.01	(0.03)	(0.01)	(0.01)	(0.50)	0.02	(0.55)	(0.14)
Total (in dollars per share)	(5.58)	4.33	0.01	1.45	16.76	2.85	1.34	2.38	0.32	22.73	9.70
Basic
Continuing operations (in dollars per share)	(5.58)	4.34	0.01	1.46	16.95	2.89	1.36	2.91	0.30	23.50	9.96
Discontinued operations (in dollars per share)	0.00	0.01	0.00	0.00	(0.03)	(0.02)	0.00	(0.50)	0.02	(0.55)	(0.14)
Total (in dollars per share)	$ (5.58)	$ 4.35	$ 0.01	$ 1.46	$ 16.92	$ 2.87	$ 1.36	$ 2.41	$ 0.32	$ 22.95	$ 9.82