CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - 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	72		89				$ (17)
Share-based compensation	90		90
Payments to noncontrolling interests	(115)							(115)
Other comprehensive income	186					186
Net income (loss)	9				(121)			130
Repurchase of common stock (shares)							(14)
Repurchase of common stock	(1,934)						$ (1,934)
Cash dividends declared	(221)				(221)
Other	0				(3)			3
Ending balance (shares) at Dec. 31, 2019		272
Ending balance (shares) at Dec. 31, 2019							(95)
Ending balance at Dec. 31, 2019	6,385	$ 3	6,614	(2)	12,075	(1,663)	$ (10,853)	211
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
Ending balance (shares) at Mar. 31, 2020		272										272
Ending balance (shares) at Mar. 31, 2020	(110)						(110)										(110)
Ending 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]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Beginning balance (shares) at Sep. 30, 2019		272
Beginning balance (shares) at Sep. 30, 2019							(92)
Beginning balance at Sep. 30, 2019	$ 6,692	$ 3	6,573	(2)	11,965	(1,704)	$ (10,353)	210
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans	11		11
Share-based compensation	30		30
Payments to noncontrolling interests	(39)							(39)
Other comprehensive income	41					41
Net income (loss)	231				186			45
Repurchase of common stock (shares)							(3)
Repurchase of common stock	(500)						$ (500)
Cash dividends declared	(73)				(73)
Other	(8)				(3)			(5)
Ending balance (shares) at Dec. 31, 2019		272
Ending balance (shares) at Dec. 31, 2019							(95)
Ending balance at Dec. 31, 2019	$ 6,385	$ 3	6,614	(2)	12,075	(1,663)	$ (10,853)	211
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	29		55				$ (26)
Share-based compensation	110		110
Payments to noncontrolling interests	(134)							(134)
Other comprehensive income	200					200
Net income (loss)	(5,085)				(5,205)			120
Exercise of put right by noncontrolling shareholders of McKesson Europe	3		3
Repurchase of common stock (shares)							(4)
Repurchase of common stock	(500)						$ (500)
Cash dividends declared	(203)				(203)
Other	$ 7		16		(6)			(3)
Ending balance (shares) at Dec. 31, 2020		273
Ending balance (shares) at Dec. 31, 2020	(114)						(114)
Ending balance at Dec. 31, 2020	$ (277)	$ 2	6,847	0	7,595	(1,503)	$ (13,418)	200
Beginning balance (shares) at Sep. 30, 2020		273
Beginning balance (shares) at Sep. 30, 2020							(112)
Beginning balance at Sep. 30, 2020	6,090	$ 2	6,780	0	13,890	(1,597)	$ (13,185)	200
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans	14		16				$ (2)
Share-based compensation	51		51
Payments to noncontrolling interests	(41)							(41)
Other comprehensive income	94					94
Net income (loss)	(6,185)				(6,226)			41
Repurchase of common stock (shares)							(2)
Repurchase of common stock	(231)						$ (231)
Cash dividends declared	(67)				(67)
Other	$ (2)				(2)
Ending balance (shares) at Dec. 31, 2020		273
Ending balance (shares) at Dec. 31, 2020	(114)						(114)
Ending balance at Dec. 31, 2020	$ (277)	$ 2	$ 6,847	$ 0	$ 7,595	$ (1,503)	$ (13,418)	$ 200