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Fair Value of Financial Instruments - Additional Information (Detail) - USD ($) | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Dealer marks of securities | 79.00% |
Percentage of carrying value for which dealer quotes were received on securities | 94.00% |
Residential Subordinate Securities |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 164,000,000 | $ 9,000,000
Commercial Loans |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 618,000,000 | 935,000,000
Guarantee Asset |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 0 | 7,000,000
Residential Senior Securities |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 236,000,000 | 72,000,000
Residential Loans |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | 10,210,000,000 | 8,810,000,000
Mortgage Servicing Rights |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 95,000,000 | $ 96,000,000
Mortgage Servicing Rights | Maximum |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Percentage difference of internal valuation than dealer marks | 1.00% |

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