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Investment in Change Healthcare Joint Venture (Details) |  |  | 3 Months Ended | 12 Months Ended |  |  |  |  |
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Mar. 09, 2020 shares | Jul. 01, 2019 USD ($) $ / shares | Mar. 31, 2020 USD ($) $ / shares | Dec. 31, 2019 USD ($) | Sep. 30, 2019 USD ($) | Jun. 30, 2019 USD ($) | Mar. 31, 2019 USD ($) $ / shares | Dec. 31, 2018 USD ($) | Sep. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Mar. 31, 2020 USD ($) $ / shares | Mar. 31, 2019 USD ($) $ / shares | Mar. 31, 2018 USD ($) | Mar. 10, 2020 $ / shares shares | Jul. 31, 2019 executive_officer | Apr. 01, 2019 USD ($) | Apr. 01, 2018 USD ($) | Mar. 31, 2017
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax gain on sale of business |  |  |  |  |  |  |  |  |  |  | $ 0 | $ 0 | $ 37,000,000 |  |  |  |  |
Cumulative effect adjustment to opening balance of retained earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 11,000,000 | $ 154,000,000 |
Equity earnings and charges from investment in Change Healthcare Joint Venture |  |  |  |  |  |  |  |  |  |  | $ (36,000,000) | $ (43,000,000) | (32,000,000) |  |  |  |  |
Shares distributed in split-off (shares) | shares | 176,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares |  |  | $ 0.01 |  |  |  | $ 0.01 |  |  |  | $ 0.01 | $ 0.01 |  |  |  |  |  |
Carrying value of equity method investments |  |  | $ 0 |  |  |  | $ 3,513,000,000 |  |  |  | $ 0 | $ 3,513,000,000 |  |  |  |  |  |
Tax Receivable Agreement (“TRA”) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of net cash tax savings realized or deemed realized under TRA (percent) |  |  | 85.00% |  |  |  |  |  |  |  | 85.00% |  |  |  |  |  |  |
Separation of Change Healthcare JV |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares distributed in split-off (shares) | shares | 176,000,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares of common stock exchanged (shares) | shares | 15,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares converted into per share converted (shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |  |
Common stock, par value (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.001 |  |  |  |
Retained Earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment to opening balance of retained earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11,000,000 | $ 154,000,000 |
Other | Tax Receivable Agreement (“TRA”) | Change Healthcare |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  |  |  |  |  | 90,000,000 |  |  |  |  |  |
After-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  |  |  |  |  | 66,000,000 |  |  |  |  |  |
Noncurrent liability |  |  | $ 0 |  |  |  | 0 |  |  |  | $ 0 | 0 |  |  |  |  |  |
Other | Operating Segments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  |  |  |  |  |  | (46,000,000) |  |  |  |  |
After-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  |  |  |  |  |  | (30,000,000) |  |  |  |  |
Change Healthcare |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity earnings and charges from investment in Change Healthcare Joint Venture |  |  | $ 44,000,000 | $ 28,000,000 | $ 51,000,000 | $ (4,000,000) | 32,000,000 | $ 50,000,000 | $ 56,000,000 | $ 56,000,000 |  |  |  |  |  |  |  |
Number of company's executive officers on joint venture's Board of Directors | executive_officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |
Change Healthcare | Technology Solutions | Core MTS Businesses | Operating Segments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax gain on sale of business |  |  |  |  |  |  |  |  |  |  |  |  | 37,000,000 |  |  |  |  |
Gain from sale of business, after tax |  |  |  |  |  |  |  |  |  |  |  |  | 22,000,000 |  |  |  |  |
Proceeds from divestiture of businesses |  |  |  |  |  |  |  |  |  |  |  |  | 126,000,000 |  |  |  |  |
Change Healthcare, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net cash proceeds from IPO |  | $ 888,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from other security offering |  | $ 279,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change Healthcare, Inc. | IPO |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Offering price (in usd per share) | $ / shares |  | $ 13 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Change Healthcare, Inc. | Change Healthcare |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest in Joint Venture (percent) |  | 41.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Contributions made in exchange for additional membership interests |  | $ 609,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate Joint Venture |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest in Joint Venture (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 70.00%
Pre-tax dilution loss |  |  |  |  | 246,000,000 |  |  |  |  |  | 246,000,000 |  |  |  |  |  |  |
After-tax dilution loss |  |  |  |  | 184,000,000 |  |  |  |  |  | 184,000,000 |  |  |  |  |  |  |
Carrying value of equity method investments |  |  |  |  |  |  | 3,500,000,000 |  |  |  |  | 3,500,000,000 |  |  |  |  |  |
Excess of carrying value over proportionate share of investment net assets |  |  |  |  |  |  | $ 4,200,000,000 |  |  |  |  | 4,200,000,000 |  |  |  |  |  |
Corporate Joint Venture | Transition Services Agreements (“TSA”) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total fees charged under the TSA |  |  |  |  |  |  |  |  |  |  | 22,000,000 | 60,000,000 | 91,000,000 |  |  |  |  |
Corporate Joint Venture | Change Healthcare |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest in Joint Venture (percent) |  | 58.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pre-tax other-than-temporary impairment |  |  |  |  | 1,200,000,000 |  |  |  |  |  | 1,200,000,000 |  |  |  |  |  |  |
After-tax other-than-temporary impairment |  |  |  |  | $ 864,000,000 |  |  |  |  |  | 864,000,000 |  |  |  |  |  |  |
Equity earnings and charges from investment in Change Healthcare Joint Venture |  |  |  |  |  |  |  |  |  |  | $ 119,000,000 | 194,000,000 | 248,000,000 |  |  |  |  |
Provisional tax benefit |  |  |  |  |  |  |  |  |  |  |  |  | $ 76,000,000 |  |  |  |  |
Pre-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  |  | (90,000,000) |  |  | (90,000,000) |  |  |  |  |  |
After-tax credit representing reduction in TRA liability |  |  |  |  |  |  |  |  | $ (66,000,000) |  |  | $ (66,000,000) |  |  |  |  |  |
Corporate Joint Venture | Change Healthcare | ASU 2014-09 | Retained Earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment to opening balance of retained earnings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 80,000,000 |  |
Corporate Joint Venture | Change Healthcare, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest in Joint Venture (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30.00%

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