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Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2014 | Sep. 30, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Dealer marks of securities | 81.00% | 81.00%
Percentage of carrying value for which dealer quotes have been received | 94.00% | 94.00%
Percentage difference of internal valuation than dealer marks | 2.00% | 2.00%
Commercial Loans |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 340 | $ 609
Commercial Secured Borrowings |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset |  | 65
Asset-backed Securities |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Dealer marks of securities | 42.00% | 42.00%
Percentage difference of internal valuation than dealer marks | 1.00% | 1.00%
Senior Securities | Residential |  |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] |  |
Fair value option elected aggregate carrying amount, asset | $ 3,310 | $ 6,120
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%

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