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Healthcare Technology Net Asset Exchange (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2016 | Mar. 01, 2017
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Carrying value of equity method investments | $ 3,728 |  |  |  | $ 4,063 | $ 3,728 | $ 4,063 |  |
Corporate Joint Venture |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Carrying value of equity method investments | 3,728 |  |  |  | 4,063 | 3,728 | 4,063 |  |
Excess of carrying value over proportionate share of investment net assets | 4,472 |  |  |  | 4,762 | 4,472 | 4,762 |  |
Core MTS Businesses | Corporate Joint Venture |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Ownership interest in Joint Venture (percent) |  |  |  |  |  |  |  |  | 70.00%
Core MTS Businesses | Technology Solutions | Operating Segments |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Pre-tax gain on sale of business |  |  |  |  | 3,947 |  | 3,947 |  |
Gain from sale of business, after tax |  |  |  |  | 3,018 |  |  |  |
Carrying value of contributed business' net assets |  |  |  |  | 1,132 |  | 1,132 |  |
Promissory notes received |  |  |  |  | $ 1,258 |  | 1,258 |  |
Transition Services Agreements (“TSA”) | Corporate Joint Venture |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Total fees charged under the TSA |  |  |  |  |  | 91 |  |  |
Change Healthcare | Tax Receivable Agreement (“TRA”) |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Noncurrent liability | 90 |  |  |  |  | 90 |  |  | $ 136
Credit in operating expense |  |  |  |  |  | 46 |  |  |
Change Healthcare |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Loss from equity method investment in Change Healthcare | $ (23) | $ 90 | $ 61 | $ 120 |  | 248 | $ 0 | $ 0 |
Change Healthcare | Corporate Joint Venture |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Loss from equity method investment in Change Healthcare |  |  |  |  |  | 248 |  |  |
Provisional tax benefit |  |  |  |  |  | $ 76 |  |  |
Change Healthcare | Core MTS Businesses | Technology Solutions | Operating Segments |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Pre-tax gain on sale of business |  |  |  | 37 |  |  |  |  |
Gain from sale of business, after tax |  |  |  | $ 22 |  |  |  |  |
Proceeds from Divestiture of Businesses |  |  | $ 126 |  |  |  |  |  |

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