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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount of unrealized gain (loss) recognized in earnings from investment in debt and equity securities measured at fair value with change in fair value recognized in net income, and recognized from transfer of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and investment in debt security measured at amortized cost (held-to-maturity) to investment in debt security measured at fair value with change in fair value recognized in net income (trading). Excludes other-than-temporary impairment (OTTI).

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

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Amount, before tax, of (gain) loss recognized for the (reversal of write-down) write-down to fair value, less cost to sell, of a disposal group. Excludes discontinued operations.

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Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process.

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Name:	us-gaap_StatementBusinessSegmentsAxis=mck_PrescriptionTechnologySolutionsSegmentMember
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Segments of Business - Narrative (Details) product in Thousands, $ in Millions			3 Months Ended			6 Months Ended	9 Months Ended	12 Months Ended
	Jul. 23, 2021 USD ($)	Mar. 09, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2021 segment	Mar. 31, 2021 segment	Mar. 31, 2022 USD ($) country product segment	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments \| segment						4	4	4
Credits associated with last-in, first-out inventory method								$ (23)	$ (38)	$ (252)
Company's International Segment Operating Loss [Abstract]
Charge for remeasurement to fair value								1,509	0	0
Goodwill impairment charge								0	69	2
Equity earnings and charges from investment in Change Healthcare Joint Venture								(43)	(48)	(36)
Corporate expenses, net [Abstract]
Net gains associated with equity investments								(98)	(133)
Corporate expenses, net								(1,073)	(8,645)	(973)
Litigation settlement charges								274	7,936	82
Loss on debt extinguishment								191	0	0
Tender Offer Notes \| Loans payable
Corporate expenses, net [Abstract]
Loss on debt extinguishment	$ 191							$ (191)
German Wholesale Business
Company's International Segment Operating Loss [Abstract]
Noncontrolling interest (percent)								30.00%
National Prescription Opiate Litigation
Corporate expenses, net [Abstract]
Loss contingency accrual, period increase (decrease)								$ 274	8,100
German Wholesale Business
Company's International Segment Operating Loss [Abstract]
Gain from sale of equity method investment								42
Held-for-sale \| U.K. Businesses (Disposal Group)
Company's International Segment Operating Loss [Abstract]
Charge for remeasurement to fair value								1,200
Held-for-sale \| E.U. Businesses (Disposal Group)
Company's International Segment Operating Loss [Abstract]
Charge for remeasurement to fair value								438
Corporate \| Held-for-sale \| U.K. Businesses (Disposal Group)
Company's International Segment Operating Loss [Abstract]
Charge for remeasurement to fair value								42
Corporate \| Held-for-sale \| E.U. Businesses (Disposal Group)
Company's International Segment Operating Loss [Abstract]
Charge for remeasurement to fair value								55
For Two Counties In re: National Prescription Opiate Litigation
Corporate expenses, net [Abstract]
Litigation settlement charges										82
Shareholder Derivative Action
Corporate expenses, net [Abstract]
Corporate expenses, net									(131)
Pension Plans, Defined Benefit \| U.S. Plans
Corporate expenses, net [Abstract]
Pre-tax pension settlement charges				$ 105	$ 17					122
Change Healthcare
Company's International Segment Operating Loss [Abstract]
Gain from sale of equity method investment		$ 414	$ 414
Corporate Joint Venture
Company's International Segment Operating Loss [Abstract]
Pre-tax dilution loss				246
Corporate Joint Venture \| Change Healthcare
Company's International Segment Operating Loss [Abstract]
Gain from sale of equity method investment			$ 414							(414)
Pre-tax other-than-temporary impairment				$ 1,200						1,200
Pre-tax dilution loss										246
Equity earnings and charges from investment in Change Healthcare Joint Venture										119
International
Company's International Segment Operating Loss [Abstract]
Charge for remeasurement to fair value									58	275
Goodwill impairment charge									69
Long-lived asset impairment charges, before tax								$ 36	$ 115	$ 112
International \| Operating Segments
Segment Reporting Information [Line Items]
Derived revenues (percent)								8.00%	8.00%	8.00%
International \| Operating Segments \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Canadian Health Benefit Claims Management and Plan Administrative Services Business
Company's International Segment Operating Loss [Abstract]
Pre-tax gain on sale of business								$ (59)
International \| Operating Segments \| Held-for-sale \| German Wholesale Business \| Walgreens Boots Alliance Joint Venture
Company's International Segment Operating Loss [Abstract]
Gain from sale of equity method investment								42
Charge for remeasurement to fair value									$ 58	$ 275
International \| Operating Segments \| Held-for-sale \| U.K. Businesses (Disposal Group)
Company's International Segment Operating Loss [Abstract]
Charge for remeasurement to fair value								1,100
International \| Operating Segments \| Held-for-sale \| E.U. Businesses (Disposal Group)
Company's International Segment Operating Loss [Abstract]
Charge for remeasurement to fair value								$ 383
International \| Europe
Segment Reporting Information [Line Items]
Number of countries in which entity operates \| country								11
U.S. Pharmaceutical
Company's International Segment Operating Loss [Abstract]
Goodwill impairment charge									0
U.S. Pharmaceutical \| New York Opioid Tax Surcharge
Segment Reporting Information [Line Items]
Charge recorded related to Company's share of the litigation settlement									$ 50
U.S. Pharmaceutical \| Operating Segments
Segment Reporting Information [Line Items]
Derived revenues (percent)								1.00%	1.00%	1.00%
Net cash proceeds from settlements								$ (46)	$ (181)	$ (22)
Medical-Surgical Solutions
Segment Reporting Information [Line Items]
Number of national brand medical surgical products \| product								285
Inventory write-down charges								$ 164	136
Company's International Segment Operating Loss [Abstract]
Goodwill impairment charge									$ 0
Medical-Surgical Solutions \| Operating Segments
Segment Reporting Information [Line Items]
Derived revenues (percent)								3.00%	3.00%	3.00%
Prescription Technology Solutions \| Operating Segments
Segment Reporting Information [Line Items]
Derived revenues (percent)								40.00%	40.00%	40.00%