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Fair Value of Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Dealer marks of securities	79.00%	79.00%
Percentage of carrying value for which dealer quotes have been received	90.00%	90.00%
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	$ 149	$ 268
Commercial Secured Borrowings
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value option elected aggregate carrying amount, asset	30	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	$ 1,740	$ 2,820
Mortgage Servicing Rights \| Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Percentage difference of internal valuation than dealer marks	2.00%	2.00%