Quarterly Financial Information (Unaudited) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 59,142	$ 62,599	$ 60,808	$ 55,679	$ 58,535	$ 59,172	$ 57,616	$ 55,728	$ 238,228	$ 231,051	$ 214,319
Gross profit	3,297	3,151	3,000	2,700	3,336	3,033	2,867	2,787	12,148	12,023	11,754
Income (loss) after income taxes:
Continuing operations	713	(6,174)	627	495	1,072	247	(676)	483	(4,339)	1,126	254
Discontinued operations	0	0	0	(1)	6	(5)	(1)	(6)	(1)	(6)	1
Net income (loss)	713	(6,174)	627	494	1,078	242	(677)	477	(4,340)	1,120	255
Net income (loss) attributable to McKesson Corporation	$ 666	$ (6,226)	$ 577	$ 444	$ 1,021	$ 186	$ (730)	$ 423	$ (4,539)	$ 900	$ 34
Diluted
Continuing operations (in dollars per share)	$ 4.15	$ (39.03)	$ 3.54	$ 2.72	$ 5.82	$ 1.06	$ (3.99)	$ 2.27	$ (28.26)	$ 4.99	$ 0.17
Discontinued operations (in dollars per share)	0	0	0	0	0.03	(0.03)	0	(0.03)	0	(0.04)	0
Total (in dollars per share)	4.15	(39.03)	3.54	2.72	5.85	1.03	(3.99)	2.24	(28.26)	4.95	0.17
Basic
Continuing operations (in dollars per share)	4.19	(39.03)	3.56	2.74	5.86	1.06	(3.99)	2.28	(28.26)	5.01	0.17
Discontinued operations (in dollars per share)	0	0	0	0	0.03	(0.02)	0	(0.03)	0	(0.03)	0
Total (in dollars per share)	$ 4.19	$ (39.03)	$ 3.56	$ 2.74	$ 5.89	$ 1.04	$ (3.99)	$ 2.25	$ (28.26)	$ 4.98	$ 0.17