Fair Value Measurement - Schedule of Assets Measured at Fair Value on Recurring Basis Quantitative Information about Level 3 Fair Value Measurements (Detail) $ in Millions	Mar. 31, 2016 USD ($) $ / SecurityLoan	Dec. 31, 2015 USD ($) $ / SecurityLoan
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	$ 40,092	$ 39,061
Consumer MSRs	59	68
Derivative Assets, Gross Amount	2,023	1,518
Fair Value Inputs [Abstract]
Derivative Credit Risk Valuation Adjustment, Derivative Assets (Liabilities)	4	4
Level 3 \| Retained interest in securitizations
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Retained interests in securitizations	201	211
Fair Value, Measurements, Recurring [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	40,092	39,061
Consumer MSRs	59	68
Derivative Assets, Gross Amount	2,023	1,518
Retained interests in securitizations	201	211
Fair Value Inputs [Abstract]
Assets, Fair Value Disclosure	42,375	40,858
Fair Value, Measurements, Recurring [Member] \| RMBS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	28,268	27,311
Fair Value, Measurements, Recurring [Member] \| CMBS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	5,504	5,379
Fair Value, Measurements, Recurring [Member] \| Other ABS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	1,038	1,340
Fair Value, Measurements, Recurring [Member] \| Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	797	615
Consumer MSRs	59	68
Derivative Assets, Gross Amount	71	57
Retained interests in securitizations	201	211
Fair Value Inputs [Abstract]
Assets, Fair Value Disclosure	1,128	951
Fair Value, Measurements, Recurring [Member] \| Level 3 \| RMBS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	$ 505	$ 504
Fair Value, Measurements, Recurring [Member] \| Level 3 \| RMBS \| Discounted cash flows \| Minimum
Fair Value Inputs [Abstract]
Yield (percent)	0.00%	0.00%
Constant prepayment rate (percent)	0.00%	0.00%
Default rate (percent)	0.00%	0.00%
Loss severity (percent)	9.00%	16.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| RMBS \| Discounted cash flows \| Maximum
Fair Value Inputs [Abstract]
Yield (percent)	15.00%	12.00%
Constant prepayment rate (percent)	27.00%	28.00%
Default rate (percent)	11.00%	8.00%
Loss severity (percent)	88.00%	85.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| RMBS \| Discounted cash flows \| Weighted Average
Fair Value Inputs [Abstract]
Yield (percent)	6.00%	6.00%
Constant prepayment rate (percent)	5.00%	4.00%
Default rate (percent)	4.00%	4.00%
Loss severity (percent)	54.00%	55.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| CMBS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	$ 251	$ 97
Fair Value, Measurements, Recurring [Member] \| Level 3 \| CMBS \| Discounted cash flows \| Minimum
Fair Value Inputs [Abstract]
Yield (percent)	1.00%	2.00%
Constant prepayment rate (percent)	0.00%	0.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| CMBS \| Discounted cash flows \| Maximum
Fair Value Inputs [Abstract]
Yield (percent)	3.00%	3.00%
Constant prepayment rate (percent)	15.00%	15.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| CMBS \| Discounted cash flows \| Weighted Average
Fair Value Inputs [Abstract]
Yield (percent)	2.00%	3.00%
Constant prepayment rate (percent)	2.00%	9.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Other ABS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	$ 30	$ 0
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Other ABS \| Discounted cash flows \| Minimum
Fair Value Inputs [Abstract]
Yield (percent)	1.00%
Constant prepayment rate (percent)	3.00%
Default rate (percent)
Loss severity (percent)
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Other ABS \| Discounted cash flows \| Maximum
Fair Value Inputs [Abstract]
Yield (percent)	1.00%
Constant prepayment rate (percent)	3.00%
Default rate (percent)
Loss severity (percent)
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Other ABS \| Discounted cash flows \| Weighted Average
Fair Value Inputs [Abstract]
Yield (percent)	1.00%
Constant prepayment rate (percent)	3.00%
Default rate (percent)
Loss severity (percent)
Fair Value, Measurements, Recurring [Member] \| Level 3 \| US Government-sponsored Enterprises Debt Securities and Other Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	$ 11	$ 14
Fair Value, Measurements, Recurring [Member] \| Level 3 \| US Government-sponsored Enterprises Debt Securities and Other Securities [Member] \| Discounted cash flows \| Minimum
Fair Value Inputs [Abstract]
Yield (percent)	1.00%	1.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| US Government-sponsored Enterprises Debt Securities and Other Securities [Member] \| Discounted cash flows \| Maximum
Fair Value Inputs [Abstract]
Yield (percent)	1.00%	1.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| US Government-sponsored Enterprises Debt Securities and Other Securities [Member] \| Discounted cash flows \| Weighted Average
Fair Value Inputs [Abstract]
Yield (percent)	1.00%	1.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Consumer MSRs
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Consumer MSRs	$ 59	$ 68
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Consumer MSRs \| Discounted cash flows \| Minimum
Fair Value Inputs [Abstract]
Total prepayment rate (percent)	10.00%	11.00%
Discount rate (percent)	15.00%	12.00%
Option adjusted spread rate (percent)	4.35%	4.35%
Servicing cost ($ per loan) \| $ / SecurityLoan	93	93
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Consumer MSRs \| Discounted cash flows \| Maximum
Fair Value Inputs [Abstract]
Total prepayment rate (percent)	20.00%	18.00%
Discount rate (percent)	15.00%	12.00%
Option adjusted spread rate (percent)	15.00%	15.00%
Servicing cost ($ per loan) \| $ / SecurityLoan	201	201
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Consumer MSRs \| Discounted cash flows \| Weighted Average
Fair Value Inputs [Abstract]
Total prepayment rate (percent)	17.00%	16.00%
Discount rate (percent)	15.00%	12.00%
Option adjusted spread rate (percent)	4.77%	4.74%
Servicing cost ($ per loan) \| $ / SecurityLoan	98	98
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Derivative assets
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Assets, Gross Amount	$ 71	$ 57
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Derivative assets \| Discounted cash flows \| Minimum
Fair Value Inputs [Abstract]
Swap rates (percent)	2.00%	2.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Derivative assets \| Discounted cash flows \| Maximum
Fair Value Inputs [Abstract]
Swap rates (percent)	2.00%	2.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Derivative assets \| Discounted cash flows \| Weighted Average
Fair Value Inputs [Abstract]
Swap rates (percent)	2.00%	2.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Retained interest in securitizations \| Discounted cash flows \| Minimum
Fair Value Inputs [Abstract]
Life of receivables (months)	14 months	16 months
Constant prepayment rate (percent)	1.00%	1.00%
Default rate (percent)	1.00%	2.00%
Loss severity (percent)	6.00%	15.00%
Discount rate (percent)	3.00%	4.00%
Fair Value, Measurements, Recurring [Member] \| Level 3 \| Retained interest in securitizations \| Discounted cash flows \| Maximum
Fair Value Inputs [Abstract]
Life of receivables (months)	83 months	75 months
Constant prepayment rate (percent)	12.00%	13.00%
Default rate (percent)	6.00%	6.00%
Loss severity (percent)	117.00%	94.00%
Discount rate (percent)	11.00%	9.00%
Derivative Financial Instruments, Liabilities [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 \| Discounted cash flows \| Minimum
Fair Value Inputs [Abstract]
Swap rates (percent)	2.00%	2.00%
Derivative Financial Instruments, Liabilities [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 \| Discounted cash flows \| Maximum
Fair Value Inputs [Abstract]
Swap rates (percent)	2.00%	2.00%
Derivative Financial Instruments, Liabilities [Member] \| Fair Value, Measurements, Recurring [Member] \| Level 3 \| Discounted cash flows \| Weighted Average
Fair Value Inputs [Abstract]
Swap rates (percent)	2.00%	2.00%

Derivative Credit Risk Valuation Adjustment, Derivative Assets (Liabilities)

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Interest rate correlation, used as an input to measure fair value.

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Fair Value Inputs, Life of Receivables

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Fair Value Inputs, Option Adjusted Spread Rate

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Fair value inputs, swap rate.

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- Definition

Rate at which loans or a loan portfolio are expected to prepay principal balances with consideration of defaults, used as an input to measure fair value

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Fair value Inputs, Servicing Cost Per Loan

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
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-Paragraph 3
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Loss, including interest and principal, incurred on a defaulted security, expressed as a percentage of the original principal balance, used as an input to measure fair value.

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-Publisher FASB
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Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

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-Name Accounting Standards Codification
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Percentage of likelihood a loan will not be repaid and instead default, used as an input to measure fair value.

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Fair value portion of interest continued to be held by a transferor after transferring financial assets to a third party.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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