Fair Value Measurements (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investment securities (Note 3)	$ 46,701,000,000	$ 43,662,000,000
Derivative assets	0	506,000,000
Derivative liabilities	67,000,000	988,000,000
Fair Value Of Securities Transferred Between Level One And Level Two		2,000,000
Cumulative Gain (Loss) Adjustment For Non Performance Risk	20,000,000	(7,000,000)
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	23,425,000,000	21,706,000,000
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	20,315,000,000	18,788,000,000
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	3,110,000,000	2,918,000,000
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	5,604,000,000	4,289,000,000
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	5,032,000,000	4,193,000,000
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	572,000,000	96,000,000
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	1,828,000,000	1,910,000,000
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	1,812,000,000	1,824,000,000
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	16,000,000	86,000,000
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	3,134,000,000	3,035,000,000
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	3,124,000,000	3,025,000,000
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	10,000,000	10,000,000
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	7,660,000,000	7,387,000,000
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	393,000,000	489,000,000
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	7,267,000,000	6,898,000,000
Foreign Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair Value Of Securities Transferred Between Level One And Level Two	17,000,000
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	1,700,000,000	1,758,000,000
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	0	61,000,000
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	711,000,000	645,000,000
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	989,000,000	1,052,000,000
Foreign Government Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair Value Of Securities Transferred Between Level One And Level Two	912,000,000
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	2,377,000,000	2,410,000,000
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	59,000,000	1,590,000,000
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	2,318,000,000	789,000,000
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	0	31,000,000
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	632,000,000	770,000,000
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	368,000,000	545,000,000
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	264,000,000	225,000,000
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	27,000,000	72,000,000
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	27,000,000	72,000,000
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	292,000,000	251,000,000
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	268,000,000	225,000,000
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	15,000,000	15,000,000
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	9,000,000	11,000,000
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	22,000,000	74,000,000
Trading [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	20,000,000	72,000,000
Trading [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	2,000,000	2,000,000
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	(7,053,000,000)	(6,546,000,000)
Derivative liabilities	(3,772,000,000)	(4,162,000,000)
Derivatives [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative assets	1,766,000,000	1,117,000,000
Derivative liabilities	32,000,000	747,000,000
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	8,684,000,000	7,493,000,000
Derivative liabilities	3,787,000,000	4,893,000,000
Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivative assets	135,000,000	170,000,000
Derivative liabilities	17,000,000	16,000,000
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	126,000,000	293,000,000
Other liabilities	22,000,000	24,000,000
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	22,000,000	24,000,000
Other 1 [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	126,000,000	293,000,000
Other liabilities	0	0
Total [Member] | Netting Adjustment Including Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	(7,053,000,000)	(6,546,000,000)
Total liabilities	(3,772,000,000)	(4,162,000,000)
Total [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	48,593,000,000	45,072,000,000
Total liabilities	54,000,000	771,000,000
Total [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	347,000,000	1,948,000,000
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	42,774,000,000	37,808,000,000
Total liabilities	3,809,000,000	4,917,000,000
Total [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	12,525,000,000	11,862,000,000
Total liabilities	$ 17,000,000	$ 16,000,000