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Quarterly Financial Information (Unaudited) - Narrative (Details) $ in Millions |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 09, 2020 USD ($) | Mar. 31, 2020 USD ($) | 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 ($) reporting_unit | Mar. 31, 2020 USD ($) | Mar. 31, 2019 USD ($) reporting_unit | Mar. 31, 2018 USD ($)
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Pretax credits related to last-in-first-out method of accounting for inventory |  | $ 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
Estimated net gain on split-off of the Change Healthcare JV |  |  |  |  |  |  |  |  |  | 0 | 56 | 43
Long-lived asset impairment charges, before tax |  |  |  |  |  | 190 |  |  | 20 | 30 |  |
Long-lived asset impairment charges, net of tax |  |  |  |  |  | 156 |  |  | 16 | 30 |  |
Proportionate share of income (loss) from Change Healthcare |  |  |  |  |  |  |  |  |  | 36 | 43 | 32
Net cash proceeds from settlements |  |  |  |  |  | 63 | 104 |  | 35 |  |  |
Goodwill impairment charge |  |  |  |  |  |  |  |  |  | 2 | $ 1,797 | 1,738
Number of reporting units | reporting_unit |  |  |  |  |  |  |  |  |  |  | 2 |
Non-cash after-tax charge |  |  |  |  |  |  |  |  |  |  |  | 1,700
Rexall Health |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-lived asset impairment charges, before tax |  |  | 32 |  |  |  |  |  |  |  |  |
Long-lived asset impairment charges, net of tax |  |  | 32 |  |  |  |  |  |  |  |  |
CANADA | Rexall Health | Third Party Seller of Rexall Health |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial 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 |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Long-lived asset impairment charges, before tax |  |  |  |  |  |  | 35 |  |  |  |  | 488
Long-lived asset impairment charges, net of tax |  |  |  |  |  |  |  |  |  |  |  | 488
European Pharmaceutical Solutions |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
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
Number of reporting units | reporting_unit |  |  |  |  |  |  |  |  | 2 |  |  |
Non-cash after-tax charge |  |  |  |  |  | 1,200 |  |  | $ 570 |  | 1,800 | 1,300
For Two Counties In re: National Prescription Opiate Litigation |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Litigation settlement charges |  |  |  | 82 |  |  |  |  |  | 82 |  |
Litigation settlement charges, after tax |  |  |  | 61 |  |  |  |  |  | 61 |  |
United States | Pension Plans, Defined Benefit |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax pension settlement charges |  |  |  | 105 | 17 |  |  |  |  | 122 |  |
After-tax pension settlement charges |  |  |  | 78 | 12 |  |  |  |  | 90 |  |
German Wholesale Joint Venture | Held-for-sale |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax impairment charge |  |  | 282 |  |  |  |  |  |  |  |  |
After-tax impairment charge |  |  | 282 |  |  |  |  |  |  |  |  |
Corporate Joint Venture |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax dilution loss |  |  |  | 246 |  |  |  |  |  | 246 |  |
After-tax dilution loss |  |  |  | 184 |  |  |  |  |  | 184 |  |
Change Healthcare |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Estimated net gain on split-off of the Change Healthcare JV | $ 414 |  |  |  |  |  |  |  |  |  |  |
Proportionate share of income (loss) from Change Healthcare |  | $ (44) | $ (28) | (51) | $ 4 | $ (32) | $ (50) | (56) | $ (56) |  |  |
Change Healthcare | Corporate Joint Venture |  |  |  |  |  |  |  |  |  |  |  |
Quarterly Financial Information [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax other-than-temporary impairment |  |  |  | 1,200 |  |  |  |  |  | 1,200 |  |
After-tax other-than-temporary impairment |  |  |  | $ 864 |  |  |  |  |  | 864 |  |
Proportionate share of income (loss) from Change Healthcare |  |  |  |  |  |  |  |  |  | $ (119) | (194) | $ (248)
Pre-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  | 90 |  |  | 90 |
After-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  | $ 66 |  |  | $ 66 |

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