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Asset-Backed Securities Issued - Additional Information (Details) - Asset-backed securities issued - USD ($) $ in Millions | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2018 | Dec. 31, 2017
Legacy Sequoia |  |
Debt Instrument [Line Items] |  |
Amortization of debt issuance costs | $ 1 | $ 1
Sequoia Choice |  |
Debt Instrument [Line Items] |  |
Amortization of debt issuance costs | $ 5 | $ 2
Contractual maturities of over five years |  |
Debt Instrument [Line Items] |  |
Contractual maturities of ABS (in years) | 5 years |

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