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Fair Value of Financial Instruments - Additional Information (Detail) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2015 USD ($) | Sep. 30, 2015 USD ($)
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Dealer marks of securities | 78.00% | 78.00%
Percentage of carrying value for which dealer quotes have been received | 91.00% | 91.00%
Mortgage servicing rights |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 23,000,000 | $ 74,000,000
Mortgage servicing rights | Maximum |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Percentage difference of internal valuation than dealer marks | 1.00% | 1.00%
Residential Subordinate Securities |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 9,000,000 | $ 68,000,000
Residential Senior Securities |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 0 | 33,000,000
Residential Loans |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 2,910,000,000 | 8,090,000,000
Commercial Loans |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 168,000,000 | $ 518,000,000

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