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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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- Definition

Fair Value, Option, Assets, Aggregate Carrying Amount During Period

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- Definition

Percentage Difference Of Internal Valuation Than Dealer Marks

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- Definition

Percentage of Carrying Value for Which Dealer Quotes Were Received on Securities

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Percentage of Third-party Dealer Quotes Received on Securities.

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