CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Other Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury	Noncontrolling Interests	Opening retained earnings adjustment: adoption of new accounting standard	Opening retained earnings adjustment: adoption of new accounting standard Retained Earnings	Adjusted balance, April 1	Adjusted balance, April 1 Common Stock	Adjusted balance, April 1 Additional Paid-in Capital	Adjusted balance, April 1 Other Capital	Adjusted balance, April 1 Retained Earnings	Adjusted balance, April 1 Accumulated Other Comprehensive Loss	Adjusted balance, April 1 Treasury	Adjusted balance, April 1 Noncontrolling Interests
Beginning balance (shares) at Mar. 31, 2019		271										271
Beginning balance (shares) at Mar. 31, 2019							(81)										(81)
Beginning balance at Mar. 31, 2019	$ 8,287	$ 3	$ 6,435	$ (2)	$ 12,409	$ (1,849)	$ (8,902)	$ 193	$ 11	$ 11	$ 8,298	$ 3	$ 6,435	$ (2)	$ 12,420	$ (1,849)	$ (8,902)	$ 193
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans (shares)		1
Issuance of shares under employee plans	61		78				$ (17)
Share-based compensation	60		60
Payments to noncontrolling interests	(76)							(76)
Other comprehensive income	145					145
Net income (loss)	(222)				(307)			85
Repurchase of common stock (shares)							(11)
Repurchase of common stock	(1,434)						$ (1,434)
Cash dividends declared	(148)				(148)
Other	8		0	0				8
Ending balance (shares) at Sep. 30, 2019		272
Ending balance (shares) at Sep. 30, 2019							(92)
Ending balance at Sep. 30, 2019	6,692	$ 3	6,573	(2)	11,965	(1,704)	$ (10,353)	210
Beginning balance (shares) at Jun. 30, 2019		271
Beginning balance (shares) at Jun. 30, 2019							(86)
Beginning balance at Jun. 30, 2019	8,068	$ 3	6,483	(1)	12,770	(1,778)	$ (9,603)	194
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans (shares)		1
Issuance of shares under employee plans	56		56				$ 0
Share-based compensation	34		34
Payments to noncontrolling interests	(37)							(37)
Other comprehensive income	74					74
Net income (loss)	(688)				(730)			42
Repurchase of common stock (shares)							(6)
Repurchase of common stock	(750)						$ (750)
Cash dividends declared	(75)				(75)
Other	10		0	(1)				11
Ending balance (shares) at Sep. 30, 2019		272
Ending balance (shares) at Sep. 30, 2019							(92)
Ending balance at Sep. 30, 2019	$ 6,692	$ 3	6,573	(2)	11,965	(1,704)	$ (10,353)	210
Beginning balance (shares) at Mar. 31, 2020		272										272
Beginning balance (shares) at Mar. 31, 2020	(110)						(110)										(110)
Beginning balance at Mar. 31, 2020	$ 5,309	$ 2	6,663	0	13,022	(1,703)	$ (12,892)	217	$ (13)	$ (13)	$ 5,296	$ 2	$ 6,663	$ 0	$ 13,009	$ (1,703)	$ (12,892)	$ 217
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans (shares)		1
Issuance of shares under employee plans	15		39				$ (24)
Share-based compensation	59		59
Payments to noncontrolling interests	(93)							(93)
Other comprehensive income	106					106
Net income (loss)	1,100				1,021			79
Exercise of put right by noncontrolling shareholders of McKesson Europe	3		3
Repurchase of common stock (shares)							(2)
Repurchase of common stock	(269)						$ (269)
Cash dividends declared	(136)				(136)
Other	$ 9		16		(4)			(3)
Ending balance (shares) at Sep. 30, 2020		273
Ending balance (shares) at Sep. 30, 2020	(112)						(112)
Ending balance at Sep. 30, 2020	$ 6,090	$ 2	6,780	0	13,890	(1,597)	$ (13,185)	200
Beginning balance (shares) at Jun. 30, 2020		272
Beginning balance (shares) at Jun. 30, 2020							(110)
Beginning balance at Jun. 30, 2020	5,653	$ 2	6,711	0	13,384	(1,735)	$ (12,916)	207
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans (shares)		1
Issuance of shares under employee plans	18		18				$ 0
Share-based compensation	36		36
Payments to noncontrolling interests	(50)							(50)
Other comprehensive income	138					138
Net income (loss)	617				577			40
Repurchase of common stock (shares)							(2)
Repurchase of common stock	(269)						$ (269)
Cash dividends declared	(69)				(69)
Other	$ 16		15		(2)			3
Ending balance (shares) at Sep. 30, 2020		273
Ending balance (shares) at Sep. 30, 2020	(112)						(112)
Ending balance at Sep. 30, 2020	$ 6,090	$ 2	$ 6,780	$ 0	$ 13,890	$ (1,597)	$ (13,185)	$ 200