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Fair Value of Financial Instruments - Additional Information (Detail) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2016 USD ($) | Jun. 30, 2016 USD ($)
Subordinate Securities |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 75 | $ 123
Residential Loans |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 1,320 | 2,510
Commercial Loans |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 0 | $ 38
Real estate securities | Maximum |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Dealer marks of securities, percentage | 73.00% | 73.00%
Percentage of carrying value for which dealer quotes have been received | 87.00% | 87.00%
Percentage difference of internal valuation than dealer marks | 1.00% | 1.00%
Mortgage servicing rights |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 11 | $ 19
Mortgage servicing rights | Maximum |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Percentage difference of internal valuation than dealer marks | 3.00% | 3.00%

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