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Arrangements with Navient Corporation (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Apr. 30, 2014
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Related Party Transactions [Abstract] |  |
Deferred taxes to be indemnified |  | $ 283
Amount remaining | $ 35 |
Remaining balance of indemnification receivable in connection with the spin-off | 27 |
Liability for uncertainty in income taxes | 25 |
Liability for uncertainty in income taxes relating to historical transactions | $ 109 |

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