Fair Value of Financial Instruments - Schedule of Assets Measured at Fair Value on Recurring Basis Quantitative Information about Level 3 Fair Value Measurements (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	$ 39,665	$ 41,800
Consumer MSRs	58	73
Derivative assets	836	959
Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	1,466	3,330
Derivative assets	51	50
Retained interests in securitizations	203	199
Recurring
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	39,665	41,800
Consumer MSRs	58	73
Derivative assets	836	959
Retained interests in securitizations	203	199
Recurring | Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	1,466	3,330
Consumer MSRs	58	69
Derivative assets	51	50
Retained interests in securitizations	203	199
Recurring | Level 3 | RMBS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	657	1,304
Recurring | 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)	0.00%	0.00%
Recurring | Level 3 | RMBS | Discounted cash flows | Maximum
Fair Value Inputs [Abstract]
Yield (percent)	23.00%	23.00%
Constant prepayment rate (percent)	23.00%	21.00%
Default rate (percent)	11.00%	18.00%
Loss severity (percent)	80.00%	95.00%
Recurring | Level 3 | RMBS | Discounted cash flows | Weighted Average
Fair Value Inputs [Abstract]
Yield (percent)	6.00%	5.00%
Constant prepayment rate (percent)	3.00%	5.00%
Default rate (percent)	5.00%	8.00%
Loss severity (percent)	49.00%	49.00%
Recurring | Level 3 | CMBS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	303	739
Recurring | Level 3 | CMBS | Discounted cash flows | Minimum
Fair Value Inputs [Abstract]
Yield (percent)	0.00%	1.00%
Constant prepayment rate (percent)	0.00%	0.00%
Recurring | Level 3 | CMBS | Discounted cash flows | Maximum
Fair Value Inputs [Abstract]
Yield (percent)	4.00%	4.00%
Constant prepayment rate (percent)	100.00%	20.00%
Recurring | Level 3 | CMBS | Discounted cash flows | Weighted Average
Fair Value Inputs [Abstract]
Yield (percent)	1.00%	2.00%
Constant prepayment rate (percent)	4.00%	3.00%
Recurring | Level 3 | Other ABS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	110	343
Recurring | Level 3 | Other ABS | Discounted cash flows | Minimum
Fair Value Inputs [Abstract]
Yield (percent)	5.00%	1.00%
Constant prepayment rate (percent)	0.00%	1.00%
Default rate (percent)	3.00%	1.00%
Loss severity (percent)	49.00%	44.00%
Recurring | Level 3 | Other ABS | Discounted cash flows | Maximum
Fair Value Inputs [Abstract]
Yield (percent)	7.00%	8.00%
Constant prepayment rate (percent)	4.00%	6.00%
Default rate (percent)	10.00%	19.00%
Loss severity (percent)	88.00%	80.00%
Recurring | Level 3 | Other ABS | Discounted cash flows | Weighted Average
Fair Value Inputs [Abstract]
Yield (percent)	6.00%	3.00%
Constant prepayment rate (percent)	3.00%	2.00%
Default rate (percent)	6.00%	12.00%
Loss severity (percent)	75.00%	69.00%
Recurring | Level 3 | U.S. government guaranteed debt and other securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Securities available for sale	$ 396	$ 944
Recurring | Level 3 | U.S. government guaranteed debt and other securities | Discounted cash flows | Minimum
Fair Value Inputs [Abstract]
Yield (percent)	1.00%	0.00%
Recurring | Level 3 | U.S. government guaranteed debt and other securities | Discounted cash flows | Maximum
Fair Value Inputs [Abstract]
Yield (percent)	3.00%	3.00%
Recurring | Level 3 | U.S. government guaranteed debt and other securities | Discounted cash flows | Weighted Average
Fair Value Inputs [Abstract]
Yield (percent)	2.00%	2.00%
Recurring | Level 3 | Consumer MSRs | Discounted cash flows | Minimum
Fair Value Inputs [Abstract]
Total prepayment rate (percent)	10.00%	9.00%
Discount rate (percent)	10.00%	10.00%
Servicing cost ($ per loan)	62.07	81.39
Recurring | Level 3 | Consumer MSRs | Discounted cash flows | Maximum
Fair Value Inputs [Abstract]
Total prepayment rate (percent)	27.00%	32.00%
Discount rate (percent)	21.00%	17.00%
Servicing cost ($ per loan)	185.22	393.52
Recurring | Level 3 | Consumer MSRs | Discounted cash flows | Weighted Average
Fair Value Inputs [Abstract]
Total prepayment rate (percent)	16.00%	14.00%
Discount rate (percent)	13.00%	11.00%
Servicing cost ($ per loan)	75.95	89.32
Recurring | Level 3 | Derivative assets | Discounted cash flows | Minimum
Fair Value Inputs [Abstract]
Swap rates (percent)	3.00%	3.00%
Recurring | Level 3 | Derivative assets | Discounted cash flows | Maximum
Fair Value Inputs [Abstract]
Swap rates (percent)	3.00%	4.00%
Recurring | Level 3 | Derivative assets | Discounted cash flows | Weighted Average
Fair Value Inputs [Abstract]
Swap rates (percent)	3.00%	4.00%
Recurring | Level 3 | Retained interest in securitizations | Discounted cash flows | Minimum
Fair Value Inputs [Abstract]
Constant prepayment rate (percent)	1.00%	2.00%
Default rate (percent)	2.00%	2.00%
Loss severity (percent)	17.00%	15.00%
Discount rate (percent)	4.00%	5.00%
Life of receivables (months)	28 months	34 months
Recurring | Level 3 | Retained interest in securitizations | Discounted cash flows | Maximum
Fair Value Inputs [Abstract]
Constant prepayment rate (percent)	11.00%	7.00%
Default rate (percent)	7.00%	7.00%
Loss severity (percent)	111.00%	89.00%
Discount rate (percent)	12.00%	14.00%
Life of receivables (months)	82 months	101 months