Quarterly Financial Information (Unaudited) - Schedule Of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 58,535	$ 59,172	$ 57,616	$ 55,728	$ 52,429	$ 56,208	$ 53,075	$ 52,607	$ 231,051	$ 214,319	$ 208,357
Gross profit	3,336	3,033	2,867	2,787	3,201	2,970	2,804	2,779	12,023	11,754	11,184
Income (Loss) After Income Taxes:
Continuing operations	1,072	247	(676)	483	(744)	527	552	(81)	1,126	254	292
Discontinued operations	6	(5)	(1)	(6)	0	(1)	1	1	(6)	1	5
Net Income	1,078	242	(677)	477	(744)	526	553	(80)	1,120	255	297
Net Income (Loss) Attributable to McKesson Corporation	$ 1,021	$ 186	$ (730)	$ 423	$ (796)	$ 469	$ 499	$ (138)	$ 900	$ 34	$ 67
Diluted
Continuing operations (in dollars per share)	$ 5.82	$ 1.06	$ (3.99)	$ 2.27	$ (4.17)	$ 2.41	$ 2.51	$ (0.69)	$ 4.99	$ 0.17	$ 0.30
Discontinued operations (in dollars per share)	0.03	(0.03)	0	(0.03)	0	(0.01)	0	0.01	(0.04)	0	0.02
Total (in dollars per share)	5.85	1.03	(3.99)	2.24	(4.17)	2.40	2.51	(0.68)	4.95	0.17	0.32
Basic
Continuing operations (in dollars per share)	5.86	1.06	(3.99)	2.28	(4.17)	2.42	2.52	(0.69)	5.01	0.17	0.30
Discontinued operations (in dollars per share)	0.03	(0.02)	0	(0.03)	0	(0.01)	0	0.01	(0.03)	0	0.02
Total (in dollars per share)	$ 5.89	$ 1.04	$ (3.99)	$ 2.25	$ (4.17)	$ 2.41	$ 2.52	$ (0.68)	$ 4.98	$ 0.17	$ 0.32