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Investment in Change Healthcare Joint Venture (Details) - USD ($) |  | 3 Months Ended | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Jul. 01, 2019 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Apr. 01, 2019 | Mar. 31, 2019 | Apr. 01, 2018 | Mar. 31, 2017
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Cumulative-effect adjustment to beginning retained earnings |  |  |  |  |  | $ 11,000,000 |  | $ 154,000,000 |
Net income (loss) from Change Healthcare |  | $ (1,454,000,000) | $ (56,000,000) | $ (1,450,000,000) | $ (112,000,000) |  |  |  |
Carrying value of investment |  | 2,167,000,000 |  | 2,167,000,000 |  |  | $ 3,513,000,000 |  |
Transition Services Agreements (“TSA”) |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Fees incurred or earned from TSA |  |  | 26,000,000 |  | 36,000,000 |  |  |  |
Noncurrent liability |  |  | 90,000,000 |  | 90,000,000 |  |  |  |
Change Healthcare JV | Tax Receivable Agreement (“TRA”) |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Noncurrent liability |  | 0 |  | 0 |  |  | 0 |  |
Joint Venture |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership interest (percent) | 58.50% |  |  |  |  |  |  |  | 70.00%
Loss expected to be recognized |  | 246,000,000 |  |  |  |  |  |  |
Loss expected to be recognized, net of tax |  | 184,000,000 |  |  |  |  |  |  |
Carrying value of investment |  | 2,167,000,000 |  | 2,167,000,000 |  |  | 3,513,000,000 |  |
Excess of carrying amount over book value of investment |  | 2,090,000,000 |  | 2,090,000,000 |  |  | $ 4,158,000,000 |  |
Pre-tax credit recognized on relief from potential future obligations |  |  | 90,000,000 |  | 90,000,000 |  |  |  |
After-tax credit recognized on relief from potential future obligations |  |  |  |  | 66,000,000 |  |  |  |
Change Healthcare JV | Joint Venture |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Pre-tax impairment charge |  | 1,157,000,000 |  |  |  |  |  |  |
After-tax impairment charge |  | 864,000,000 |  |  |  |  |  |  |
Net income (loss) from Change Healthcare |  | $ (51,000,000) | $ (56,000,000) | $ (47,000,000) | $ (112,000,000) |  |  |  |
Retained Earnings |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Cumulative-effect adjustment to beginning retained earnings |  |  |  |  |  | 11,000,000 |  | $ 154,000,000 |
Change Healthcare, Inc. |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
IPO cash proceeds | $ 888,000,000 |  |  |  |  |  |  |  |
Proceeds from concurrent offering of other securities | 279,000,000 |  |  |  |  |  |  |  |
Change Healthcare, Inc. | Joint Venture |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership interest (percent) |  |  |  |  |  |  |  |  | 30.00%
Change Healthcare, Inc. | Change Healthcare JV |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership interest (percent) |  | 41.50% |  | 41.50% |  |  |  |  |
Contributions made in exchange of additional interest | $ 609,000,000 |  |  |  |  |  |  |  |
ASU 2014-09 | Retained Earnings | Change Healthcare JV | Joint Venture |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Cumulative-effect adjustment to beginning retained earnings |  |  |  |  |  | $ 80,000,000 |  |  |
Initial public offering | Change Healthcare, Inc. |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Offering price | $ 13 |  |  |  |  |  |  |  |

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