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Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	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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