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Segments of Business - Narrative (Details) $ in Millions |  | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
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%

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