Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investment securities (Note 3)	$ 46,500	$ 43,662
Cumulative Gain (Loss) Adjustment For Non Performance Risk	18	(7)
Domestic Corporate Debt Securities [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Domestic Corporate Debt Securities [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	23,219	21,706
Domestic Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Domestic Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	20,093	18,788
Domestic Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	3,126	2,918
US States and Political Subdivisions Debt Securities [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
US States and Political Subdivisions Debt Securities [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	5,545	4,289
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	4,985	4,193
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	560	96
Residential Mortgage Backed Securities [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Residential Mortgage Backed Securities [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	1,878	1,910
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	1,812	1,824
Residential Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	66	86
Commercial Mortgage Backed Securities [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Commercial Mortgage Backed Securities [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	3,098	3,035
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	3,086	3,025
Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	12	10
Asset-backed Securities [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Asset-backed Securities [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	7,682	7,387
Asset-backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Asset-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	405	489
Asset-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	7,277	6,898
Foreign Corporate Debt Securities [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Foreign Corporate Debt Securities [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	1,795	1,758
Foreign Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	51	61
Foreign Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	702	645
Foreign Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	1,042	1,052
Foreign Government Debt Securities [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Foreign Government Debt Securities [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	2,126	2,410
Foreign Government Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	1,323	1,590
Foreign Government Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	802	789
Foreign Government Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	1	31
US Treasury and Government [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
US Treasury and Government [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	747	770
US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	498	545
US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	249	225
Retained Interest [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Retained Interest [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	73	72
Retained Interest [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Retained Interest [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Retained Interest [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	73	72
Available-for-sale Securities [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Available-for-sale Securities [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	284	251
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	260	225
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	15	15
Available-for-sale Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	9	11
Trading [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Trading [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	53	74
Trading [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	51	72
Trading [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	2	2
Trading [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
Derivatives [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative assets	(5,938)	(6,546)
Derivative liabilities	(3,108)	(4,162)
Derivatives [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative assets	1,122	1,117
Derivative liabilities	262	747
Derivatives [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative assets	6,909	7,493
Derivative liabilities	3,352	4,893
Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative assets	151	170
Derivative liabilities	18	16
Other 1 [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	0	0
Other liabilities	0	0
Other 1 [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	140	293
Other liabilities	22	24
Other 1 [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	0	0
Other liabilities	0	0
Other 1 [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	0	0
Other liabilities	22	24
Other 1 [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	140	293
Other liabilities	0	0
Total [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	(5,938)	(6,546)
Total liabilities	(3,108)	(4,162)
Total [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	47,762	45,072
Total liabilities	284	771
Total [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	1,685	1,948
Total liabilities	0	0
Total [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	39,309	37,808
Total liabilities	3,374	4,917
Total [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	12,706	11,862
Total liabilities	$ 18	$ 16