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Segments of Business - Narrative (Details) $ in Millions |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 09, 2020 USD ($) | Mar. 31, 2020 USD ($) country | Dec. 31, 2019 USD ($) | Sep. 30, 2019 USD ($) | Jun. 30, 2019 USD ($) | Mar. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Sep. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Mar. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Mar. 31, 2020 USD ($) segment country | Mar. 31, 2019 USD ($) | Mar. 31, 2018 USD ($)
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of reportable segments | segment |  |  |  |  |  |  |  |  |  |  |  | 3 |  |
Credits associated with last-in, first-out inventory method |  | $ 138 | $ 66 | $ 33 | $ 15 | $ 146 | $ 21 | $ 22 | $ 21 |  |  | $ 252 | $ 210 | $ 99
Pretax credits related to last-in-first-out method of accounting for inventory, after tax |  | 101 | 49 | 25 | 11 | 109 | 15 | 17 | 15 |  |  | 186 | 156 | 64
Net cash proceeds from settlements |  |  |  |  |  | 63 | 104 |  | 35 |  |  |  |  |
Pre-tax charges related to customer bankruptcy |  |  |  |  |  |  |  |  |  |  |  |  | 61 |
After-tax charges related to customer bankruptcy |  |  |  |  |  |  |  |  |  |  |  |  | 45 |
Gain from sale of equity method investment, pre-tax |  |  |  |  |  |  |  |  |  |  |  | 0 | 56 | 43
Long-lived asset impairment charges, before tax |  |  |  |  |  | 190 |  |  | 20 |  |  | 30 |  |
Long-lived asset impairment charges, net of tax |  |  |  |  |  | 156 |  |  | 16 |  |  | 30 |  |
Goodwill impairment charge |  |  |  |  |  |  |  |  |  |  |  | 2 | 1,797 | 1,738
Non-cash after-tax charge |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,700
Equity earnings and charges from investment in Change Healthcare Joint Venture |  |  |  |  |  |  |  |  |  |  |  | (36) | (43) | (32)
Pre-tax gain on sale of business |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 | 37
Employee Severance and Other Exit Related Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax charge |  |  |  |  |  |  |  |  |  |  |  |  | 94 |
Restructuring charges, after tax |  |  |  |  |  |  |  |  |  |  |  |  | 70 |
Held-for-sale | Enterprise Information Solutions |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax gain on sale of business |  |  |  |  |  |  |  |  |  |  | $ 109 |  |  | 109
Gain from sale of business, after tax |  |  |  |  |  |  |  |  |  |  | $ 30 |  |  | 30
For Two Counties In re: National Prescription Opiate Litigation |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Litigation settlement charges |  |  |  | 82 |  |  |  |  |  |  |  | 82 |  |
Litigation settlement charges, after tax |  |  |  | 61 |  |  |  |  |  |  |  | 61 |  |
United States | Pension Plans, Defined Benefit |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax pension settlement charges |  |  |  | 105 | 17 |  |  |  |  |  |  | 122 |  |
After-tax pension settlement charges |  |  |  | 78 | 12 |  |  |  |  |  |  | 90 |  |
Rexall Health |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-lived asset impairment charges, before tax |  |  | 32 |  |  |  |  |  |  |  |  |  |  |
Long-lived asset impairment charges, net of tax |  |  | 32 |  |  |  |  |  |  |  |  |  |  |
Rexall Health | Third Party Seller of Rexall Health | CANADA |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from escrow settlement related to previous Acquisition |  |  |  |  |  |  |  |  | 97 |  |  |  | 97 |
Proceeds from escrow settlement related to previous Acquisition, after tax |  |  |  |  |  |  |  |  | 97 |  |  |  | 97 |
Rexall Health |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-lived asset impairment charges, before tax |  |  |  |  |  |  | 35 |  |  |  |  |  |  | 488
Long-lived asset impairment charges, net of tax |  |  |  |  |  |  |  |  |  |  |  |  |  | 488
Change Healthcare |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain from sale of equity method investment, pre-tax | $ 414 |  |  |  |  |  |  |  |  |  |  |  |  |
Equity earnings and charges from investment in Change Healthcare Joint Venture |  | $ 44 | 28 | 51 | $ (4) | 32 | 50 | 56 | 56 |  |  |  |  |
Corporate Joint Venture |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax dilution loss |  |  |  | 246 |  |  |  |  |  |  |  | 246 |  |
After-tax dilution loss |  |  |  | 184 |  |  |  |  |  |  |  | 184 |  |
Corporate Joint Venture | Change Healthcare |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax other-than-temporary impairment |  |  |  | 1,200 |  |  |  |  |  |  |  | 1,200 |  |
After-tax other-than-temporary impairment |  |  |  | $ 864 |  |  |  |  |  |  |  | 864 |  |
Pre-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  | 90 |  |  |  |  | 90 |
After-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  | $ 66 |  |  |  |  | 66 |
Equity earnings and charges from investment in Change Healthcare Joint Venture |  |  |  |  |  |  |  |  |  |  |  | 119 | 194 | 248
Customer relationships | Rexall Health | Intangible Asset and Store Assets Impairment |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-lived asset impairment charges, before tax |  |  |  |  |  |  |  |  |  |  |  | 32 | 56 |
Long-lived asset impairment charges, net of tax |  |  |  |  |  |  |  |  |  |  |  | 32 | 56 |
U.S. Pharmaceutical and Specialty Solutions |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain from sale of equity method investment, pre-tax |  |  |  |  |  |  |  |  |  |  |  |  |  | 43
Gain from sale of equity method investment, after tax |  |  |  |  |  |  |  |  |  |  |  |  |  | 26
Goodwill impairment charge |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 |
U.S. Pharmaceutical and Specialty Solutions | Operating Segments |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net cash proceeds from settlements |  |  |  |  |  |  |  |  |  |  |  | $ 22 | 202 | 144
European Pharmaceutical Solutions |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of countries in which entity operates | country |  | 13 |  |  |  |  |  |  |  |  |  | 13 |  |
Charge for remeasurement to fair value |  |  |  |  |  |  |  |  |  |  |  | $ 275 |  |
Charge for remeasurement to fair value, after tax |  |  |  |  |  |  |  |  |  |  |  | 275 |  |
Long-lived asset impairment charges, before tax |  |  | 64 |  |  |  |  |  |  |  |  | 82 | 210 | 446
Long-lived asset impairment charges, net of tax |  |  | $ 53 |  |  |  |  |  |  |  |  | 66 | 172 | 410
Goodwill impairment charge |  |  |  |  |  | 1,200 |  |  | 570 |  |  | 0 | 1,776 | 1,300
Non-cash after-tax charge |  |  |  |  |  | $ 1,200 |  |  | $ 570 |  |  |  | 1,800 | 1,300
Medical-Surgical Solutions |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill impairment charge |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 |
Other |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain from sale of equity method investment, pre-tax |  |  |  |  |  |  |  |  |  |  |  |  | 56 |
Gain from sale of equity method investment, after tax |  |  |  |  |  |  |  |  |  |  |  |  | 41 |
Goodwill impairment charge |  |  |  |  |  |  |  |  |  |  |  | 2 | 21 |
Pre-tax charge |  |  |  |  |  |  |  |  |  |  |  |  | 91 |
Restructuring charges, after tax |  |  |  |  |  |  |  |  |  |  |  |  | $ 86 |
Other | Operating Segments |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  |  |  |  |  |  |  | 46
After-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 30
Other | Rexall Health |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill impairment charge |  |  |  |  |  |  | $ 21 |  |  | $ 455 |  |  |  |
Other | Change Healthcare |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain from sale of equity method investment, pre-tax |  | $ 414 |  |  |  |  |  |  |  |  |  | 414 |  |
Gain from sale of equity method investment, after tax |  | $ 414 |  |  |  |  |  |  |  |  |  | $ 414 |  |
Services | U.S. Pharmaceutical and Specialty Solutions | Product Concentration Risk | Revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of total revenue (less than) (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 1.00% | 1.00% | 1.00%
Services | European Pharmaceutical Solutions | Product Concentration Risk | Revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of total revenue (less than) (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 10.00% | 10.00% | 10.00%
Services | Medical-Surgical Solutions | Product Concentration Risk | Revenues |  |  |  |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of total revenue (less than) (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 2.00% | 2.00% | 2.00%

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