Fair Value of Financial Instruments - Schedule of Assets and Liabilities 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, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets	$ 44,404	$ 66,086
Retained Interest in Securitization and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets	201	204
Retained Interest in Securitization and Other [Member] | Discounted Cash Flows [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	4.88%	13.52%
Retained Interest in Securitization and Other [Member] | Discounted Cash Flows [Member] | Default Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	4.80%
Retained Interest in Securitization and Other [Member] | Discounted Cash Flows [Member] | Loss Severity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	21.98%
Retained Interest in Securitization and Other [Member] | Discounted Cash Flows [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	13.19%	12.70%
Retained Interest in Securitization and Other [Member] | Minimum [Member] | Discounted Cash Flows [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life of receivables (months)	37 months	29 months
Retained Interest in Securitization and Other [Member] | Minimum [Member] | Discounted Cash Flows [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	1.63%	1.25%
Retained Interest in Securitization and Other [Member] | Minimum [Member] | Discounted Cash Flows [Member] | Default Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	1.56%
Retained Interest in Securitization and Other [Member] | Minimum [Member] | Discounted Cash Flows [Member] | Loss Severity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	14.82%
Retained Interest in Securitization and Other [Member] | Minimum [Member] | Discounted Cash Flows [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	4.25%	2.90%
Retained Interest in Securitization and Other [Member] | Maximum [Member] | Discounted Cash Flows [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life of receivables (months)	105 months	243 months
Retained Interest in Securitization and Other [Member] | Maximum [Member] | Discounted Cash Flows [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	6.71%	22.21%
Retained Interest in Securitization and Other [Member] | Maximum [Member] | Discounted Cash Flows [Member] | Default Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	7.37%
Retained Interest in Securitization and Other [Member] | Maximum [Member] | Discounted Cash Flows [Member] | Loss Severity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	89.45%
Retained Interest in Securitization and Other [Member] | Maximum [Member] | Discounted Cash Flows [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	13.57%	13.57%
Retained Interest in Securitization and Other [Member] | Average [Member] | Discounted Cash Flows [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Life of receivables (months)	83 months	66 months
Mortgage Servicing Rights [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets	58	55
Mortgage Servicing Rights [Member] | Servicing Cost ($ Per Loan) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing cost	93	302
Mortgage Servicing Rights [Member] | Discounted Cash Flows [Member] | Total Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	18.83%	19.37%
Mortgage Servicing Rights [Member] | Discounted Cash Flows [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	10.57%	12.66%
Mortgage Servicing Rights [Member] | Minimum [Member] | Servicing Cost ($ Per Loan) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing cost	85	81
Mortgage Servicing Rights [Member] | Minimum [Member] | Discounted Cash Flows [Member] | Total Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	8.18%	11.77%
Mortgage Servicing Rights [Member] | Minimum [Member] | Discounted Cash Flows [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	9.95%	9.95%
Mortgage Servicing Rights [Member] | Maximum [Member] | Servicing Cost ($ Per Loan) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing cost	420	864
Mortgage Servicing Rights [Member] | Maximum [Member] | Discounted Cash Flows [Member] | Total Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	32.52%	32.99%
Mortgage Servicing Rights [Member] | Maximum [Member] | Discounted Cash Flows [Member] | Discount Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	17.07%	37.88%
Residential Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets	1,321	1,335
Residential Mortgage-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	5.00%	5.00%
Residential Mortgage-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	5.00%	6.00%
Residential Mortgage-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Default Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	8.00%	9.00%
Residential Mortgage-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Loss Severity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	50.00%	52.00%
Residential Mortgage-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	1.00%	0.00%
Residential Mortgage-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	0.00%	0.00%
Residential Mortgage-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Default Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	0.00%	0.00%
Residential Mortgage-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Loss Severity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	0.00%	4.00%
Residential Mortgage-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	25.00%	24.00%
Residential Mortgage-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	45.00%	26.00%
Residential Mortgage-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Default Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	22.00%	21.00%
Residential Mortgage-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Loss Severity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	85.00%	75.00%
Commercial Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets	304	587
Commercial Mortgage-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	3.00%	2.00%
Commercial Mortgage-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	13.00%	11.00%
Commercial Mortgage-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	2.00%	1.00%
Commercial Mortgage-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	0.00%	0.00%
Commercial Mortgage-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	4.00%	3.00%
Commercial Mortgage-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	20.00%	15.00%
Other Asset-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets	313	102
Other Asset-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	4.00%	4.00%
Other Asset-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	3.00%	2.00%
Other Asset-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Default Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	12.00%	15.00%
Other Asset-Backed Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Loss Severity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	67.00%	72.00%
Other Asset-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	3.00%	1.00%
Other Asset-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	0.00%	0.00%
Other Asset-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Default Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	0.00%	1.00%
Other Asset-Backed Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Loss Severity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	0.00%	46.00%
Other Asset-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	8.00%	24.00%
Other Asset-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Constant Prepayment Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	24.00%	5.00%
Other Asset-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Default Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	20.00%	28.00%
Other Asset-Backed Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Loss Severity [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	88.00%	88.00%
U.S. Government Guaranteed Debt and Other Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets	964	665
U.S. Government Guaranteed Debt and Other Securities [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	2.00%	2.00%
U.S. Government Guaranteed Debt and Other Securities [Member] | Minimum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	2.00%	1.00%
U.S. Government Guaranteed Debt and Other Securities [Member] | Maximum [Member] | Discounted Cash Flows (3rd Party Pricing) [Member] | Yield [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	3.00%	4.00%
Derivative Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets	54	90
Derivative Assets [Member] | Discounted Cash Flows [Member] | Swap Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	3.36%	2.46%
Derivative Assets [Member] | Minimum [Member] | Discounted Cash Flows [Member] | Swap Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	2.76%	1.82%
Derivative Assets [Member] | Maximum [Member] | Discounted Cash Flows [Member] | Swap Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	3.47%	2.58%
Derivative Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Liabilities	$ 39	$ 38
Derivative Liabilities [Member] | Discounted Cash Flows [Member] | Swap Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted Average	3.34%	2.42%
Derivative Liabilities [Member] | Minimum [Member] | Discounted Cash Flows [Member] | Swap Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	2.76%	1.82%
Derivative Liabilities [Member] | Maximum [Member] | Discounted Cash Flows [Member] | Swap Rates [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	3.43%	2.55%