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Segments of Business - Narrative (Details) $ in Millions		3 Months Ended					9 Months Ended	12 Months Ended
Segments of Business - Narrative (Details) $ in Millions	Mar. 09, 2020 USD ($)	Sep. 30, 2020 segment	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2021 segment country numberOfProducts	Mar. 31, 2021 USD ($) country numberOfProducts	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments \| segment		4					4
Credits associated with last-in, first-out inventory method								$ 38	$ 252	$ 210
Goodwill impairment charge								69	2	1,797
Net gain from sale of equity method investment, pre-tax								0	0	56
Equity earnings and charges from investment in Change Healthcare Joint Venture								(48)	(36)	(43)
Net gains associated with equity investments								133
Corporate Expenses, Net								(8,645)	(973)	(639)
National Prescription Opiate Litigation
Segment Reporting Information [Line Items]
Charge recorded related to Company's share of the litigation settlement								8,100
For Two Counties In re: National Prescription Opiate Litigation
Segment Reporting Information [Line Items]
Litigation settlement charges									82
Shareholder Derivative Action
Segment Reporting Information [Line Items]
Corporate Expenses, Net								131
UNITED STATES \| Pension Plans, Defined Benefit
Segment Reporting Information [Line Items]
Pre-tax pension settlement charges				$ 105	$ 17				122
Change Healthcare
Segment Reporting Information [Line Items]
Net gain from sale of equity method investment, pre-tax	$ 414
Corporate Joint Venture
Segment Reporting Information [Line Items]
Pre-tax dilution loss				246
Corporate Joint Venture \| Change Healthcare
Segment Reporting Information [Line Items]
Pre-tax other-than-temporary impairment				$ 1,200					1,200
Net gain from sale of equity method investment, pre-tax			$ 414
Pre-tax dilution loss									246
Pre-tax credit representing reduction in TRA liability										90
Equity earnings and charges from investment in Change Healthcare Joint Venture									119	194
International
Segment Reporting Information [Line Items]
Long-lived asset impairment charges, before tax								115	112	245
Goodwill impairment, after tax								69		1,800
Goodwill impairment charge								69	2	$ 1,776
International \| German Wholesale Business
Segment Reporting Information [Line Items]
After-tax loss on sale of business								58	275
Pre-tax loss on sale of business								58	$ 275
International \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| German Wholesale Business
Segment Reporting Information [Line Items]
Pre-tax other-than-temporary impairment								58
After-tax other-than-temporary impairment								$ 58
International \| Operating Segments
Segment Reporting Information [Line Items]
Derived revenues (percent)								7.00%	7.00%	7.00%
International \| Europe
Segment Reporting Information [Line Items]
Number of countries in which entity operates \| country							13	13
International \| Rexall Health \| Third Party Seller of Rexall Health \| Canada
Segment Reporting Information [Line Items]
Proceeds from escrow settlement related to previous Acquisition										$ 97
International \| Rexall Health
Segment Reporting Information [Line Items]
Long-lived asset impairment charges, before tax									$ 30
Goodwill impairment charge						$ 21
U.S. Pharmaceutical
Segment Reporting Information [Line Items]
Pre-tax charges related to customer bankruptcy										$ 61
Goodwill impairment charge								$ 0	$ 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								$ 181	$ 22	$ 202
Medical-Surgical Solutions
Segment Reporting Information [Line Items]
Number of national brand medical surgical products \| numberOfProducts							275,000	275,000
Goodwill impairment charge								$ 0	$ 0
Inventory write-down charges								$ 136
Medical-Surgical Solutions \| Operating Segments
Segment Reporting Information [Line Items]
Derived revenues (percent)								2.00%	2.00%	2.00%
Prescription Technology Solutions
Segment Reporting Information [Line Items]
Goodwill impairment charge								$ 0	$ 0
Net gain from sale of equity method investment, pre-tax										$ 56
Prescription Technology Solutions \| Operating Segments
Segment Reporting Information [Line Items]
Derived revenues (percent)								39.00%	39.00%	39.00%