CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury	Noncontrolling Interests	Opening retained earnings adjustments: adoption of new accounting standard	Opening retained earnings adjustments: 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 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, 2020		272									272
Beginning balance (shares) at Mar. 31, 2020						(110)									(110)
Beginning balance at Mar. 31, 2020	$ 5,309	$ 2	$ 6,663	$ 13,022	$ (1,703)	$ (12,892)	$ 217	$ (13)	$ (13)	$ 5,296	$ 2	$ 6,663	$ 13,009	$ (1,703)	$ (12,892)	$ 217
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans, net of forfeitures (shares)		1
Issuance of shares under employee plans, net of forfeitures	15		39			$ (24)
Share-based compensation	59		59
Payments to noncontrolling interests	(93)						(93)
Other comprehensive loss	106				106
Net income	1,100			1,021			79
Repurchase of common stock (in shares)						(2)
Repurchase of common stock	(269)					$ (269)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	3		3
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)
Ending balance at Sep. 30, 2020	6,090	$ 2	6,780	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	13,384	(1,735)	$ (12,916)	207
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans, net of forfeitures (shares)		1
Issuance of shares under employee plans, net of forfeitures	18		18
Share-based compensation	36		36
Payments to noncontrolling interests	(50)						(50)
Other comprehensive loss	138				138
Net income	617			577			40
Repurchase of common stock (in 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)
Ending balance at Sep. 30, 2020	$ 6,090	$ 2	6,780	13,890	(1,597)	$ (13,185)	200
Beginning balance (shares) at Mar. 31, 2021		273
Beginning balance (shares) at Mar. 31, 2021	(115)					(115)
Beginning balance at Mar. 31, 2021	$ 175	$ 2	6,925	8,202	(1,480)	$ (13,670)	196
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans, net of forfeitures (shares)		2
Issuance of shares under employee plans, net of forfeitures	51		111			$ (60)
Share-based compensation	76		76
Payments to noncontrolling interests	(79)						(79)
Other comprehensive loss	(15)				(15)
Net income	835			753			82
Repurchase of common stock (in shares)						(7)
Repurchase of common stock	(1,280)		21			$ (1,301)
Exercise of put right by noncontrolling shareholders of McKesson Europe AG	8		178		(170)
Reclassification of McKesson Europe redeemable noncontrolling interests	287						287
Reclassification of recurring compensation to other accrued liabilities	(2)						(2)
Cash dividends declared	(139)			(139)
Other	$ (4)			(4)
Ending balance (shares) at Sep. 30, 2021		275
Ending balance (shares) at Sep. 30, 2021	(122)					(122)
Ending balance at Sep. 30, 2021	$ (87)	$ 2	7,311	8,812	(1,665)	$ (15,031)	484
Beginning balance (shares) at Jun. 30, 2021		274
Beginning balance (shares) at Jun. 30, 2021						(119)
Beginning balance at Jun. 30, 2021	(45)	$ 2	7,057	8,618	(1,627)	$ (14,579)	484
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares under employee plans, net of forfeitures (shares)		1
Issuance of shares under employee plans, net of forfeitures	39		40			$ (1)
Share-based compensation	43		43
Payments to noncontrolling interests	(40)						(40)
Other comprehensive loss	(38)				(38)
Net income	310			267			43
Repurchase of common stock (in shares)						(3)
Repurchase of common stock	(280)		171			$ (451)
Reclassification of recurring compensation to other accrued liabilities	(2)						(2)
Cash dividends declared	(74)			(74)
Other	$ 0			1			(1)
Ending balance (shares) at Sep. 30, 2021		275
Ending balance (shares) at Sep. 30, 2021	(122)					(122)
Ending balance at Sep. 30, 2021	$ (87)	$ 2	$ 7,311	$ 8,812	$ (1,665)	$ (15,031)	$ 484