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Income Taxes - Narrative (Details) - USD ($) $ in Millions |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Mar. 09, 2020 | Mar. 31, 2020 | Mar. 31, 2021 | Mar. 31, 2020 | Mar. 31, 2019 | Mar. 31, 2018
Income Tax Contingency [Line Items] |  |  |  |  |  |
Income tax expense (benefit) rates (percent) |  |  | (13.80%) | 1.60% | 58.40% |
Statutory federal income tax rate (percent) |  |  |  | 21.00% | 21.00% |
Research and development credit |  |  | $ 5 | $ 7 | $ 7 |
Impact of opioid-related claims |  |  | 8,100 |  |  |
After-tax impact of opioid-related claims |  |  | 6,800 |  |  |
Deferred tax benefit |  |  | 908 | 342 | (189) |
Unrecognized tax benefits |  |  |  | (91) |  |
Net discrete tax benefit |  |  | 105 |  | 42 |
Net gain from sale of equity method investment, pre-tax |  |  | 0 | 0 | 56 |
Non-cash pre-tax charge |  |  | 69 | 2 | 1,797 |
Valuation allowance |  | $ 833 | 864 | 833 |  |
Increase (decrease) in valuation allowance |  |  | 31 |  |  |
Unrecognized tax benefits |  | 958 | 1,754 | 958 | 1,052 | $ 1,183
Unrecognized tax benefits that would Impact income tax expense and the effective tax rate |  |  | 1,300 |  |  |
Decrease in unrecognized tax benefits |  |  |  | 91 |  |
Amount of decrease in unrecognized tax benefits that is reasonably possible in the next twelve months |  |  | 93 |  |  |
Income tax expense (benefit), before any tax effect, related to accrued interest and penalties |  |  | 9 | 23 | 33 |
Accrued interest and penalties on unrecognized tax benefits |  | 91 | 101 | 91 |  |
Undistributed earnings of foreign operations |  |  | 6,000 |  |  |
Change Healthcare |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Net gain from sale of equity method investment, pre-tax | $ 414 |  |  |  |  |
Change Healthcare | Corporate Joint Venture |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Net gain from sale of equity method investment, pre-tax |  | $ 414 |  |  |  |
Federal |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Federal, state and foreign net operating loss carryforwards |  |  | 2,400 |  |  |
State |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Federal, state and foreign net operating loss carryforwards |  |  | 3,900 |  |  |
Foreign Tax Authority |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Federal, state and foreign net operating loss carryforwards |  |  | 2,200 |  |  |
International |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Charge for remeasurement to fair value |  |  |  | 275 |  |
Non-cash pre-tax charge |  |  | 69 | $ 2 | $ 1,776 |
Pending and Future Opioid-Related Claims |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Deferred tax benefit |  |  | 1,300 |  |  |
Unrecognized tax benefits |  |  | 455 |  |  |
Decrease in unrecognized tax benefits |  |  | (455) |  |  |
Capital Loss Carryforward | Foreign Tax Authority |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Federal, state and foreign net operating loss carryforwards |  |  | $ 783 |  |  |

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