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Business Acquisitions and Divestitures - Acquisitions (Details) - USD ($) $ in Millions			3 Months Ended	9 Months Ended
	Nov. 01, 2022	Oct. 31, 2022	Dec. 31, 2023	Dec. 31, 2023	Mar. 31, 2023
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill			$ 9,973	$ 9,973	$ 9,947
RxTs Segment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair value adjustment gain			2	78
U.S. Pharmaceutical
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill			4,043	4,043	4,050
Rx Savings Solutions, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair value adjustment gain			2	78
Rx Savings Solutions, LLC \| RxTs Segment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business acquisition, percentage of controlling interest in combined business	100.00%
Cash payments to acquire business	$ 600
Contingent consideration	92
Other current liabilities			$ 14	$ 14	83
Other non-current liabilities					$ 9
Acquired identifiable intangible assets	$ 229
Weighted average life of intangibles	12 years
Goodwill	$ 463
Rx Savings Solutions, LLC \| RxTs Segment \| Maximum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contingent consideration	$ 275
SCRI Oncology, LLC \| U.S. Pharmaceutical
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business acquisition, percentage of controlling interest in combined business		51.00%
Cash payments to acquire business		$ 166
Acquired identifiable intangible assets		$ 177
Weighted average life of intangibles		17 years
Goodwill		$ 113
Goodwill, expected tax deductible amount		46
Noncontrolling interest		225
SCRI Oncology, LLC \| U.S. Pharmaceutical \| SCRI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Noncontrolling interest		202
SCRI Oncology, LLC \| U.S. Pharmaceutical \| USOR
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Noncontrolling interest		$ 23