Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investment securities (Note 3)	$ 47,906	$ 47,359
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investment securities (Note 3)	0
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	21,298	20,535
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	3,372	3,235
Domestic Corporate Debt Securities [Member] | Netting Adjustment [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	24,670	23,770
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	3,051	2,824
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	0	4
Commercial Mortgage Backed Securities [Member] | Netting Adjustment [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	3,051	2,828
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
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	3,688	3,157
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	81	77
US States and Political Subdivisions Debt Securities [Member] | Netting Adjustment [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	3,769	3,234
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	72	71
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	1,129	1,058
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	1,363	1,204
Foreign Corporate Debt Securities [Member] | Netting Adjustment [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	2,564	2,333
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	825	930
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	4,304	4,040
Asset-backed Securities [Member] | Netting Adjustment [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	5,129	4,970
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	874	1,003
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	974	1,444
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	51	84
Foreign Government Debt Securities [Member] | Netting Adjustment [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	1,899	2,531
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	3,241	3,805
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	261	253
US Treasury and Government [Member] | Netting Adjustment [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	3,502	4,058
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	31	35
Retained Interest [Member] | Netting Adjustment [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	31	35
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	566	715
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	14	18
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	14	17
Available-for-sale Securities [Member] | Netting Adjustment [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	594	750
Trading [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	260	241
Trading [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Investments, Fair Value Disclosure	0	0
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
Trading [Member] | Netting Adjustment [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	260	241
Derivatives [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivatives	0	0
Derivative Assets	0	0
Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivatives	4,217	4,503
Derivative Assets	12,265	14,830
Derivatives [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivatives	14	20
Derivative Assets	148	160
Derivatives [Member] | Netting Adjustment [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivatives	(3,516)	(4,025)
Derivative Assets	(6,653)	(5,319)
Derivatives [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Derivatives	715	498
Derivative Assets	5,760	9,671
Other [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 [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	0	0
Other liabilities	23	25
Other [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	409	388
Other liabilities	0	0
Other [Member] | Netting Adjustment [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	0	0
Other liabilities	0	0
Other [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Other assets	409	388
Other liabilities	23	25
Total [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	1,772	2,030
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	48,825	51,169
Total liabilities	4,240	4,528
Total [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	10,131	9,538
Total liabilities	14	20
Total [Member] | Netting Adjustment [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	(6,653)	(5,319)
Total liabilities	(3,516)	(4,025)
Total [Member] | Net Balance [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Total assets	54,075	57,418
Total liabilities	738	523
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	2,340	2,568
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	97	41
Residential Mortgage Backed Securities [Member] | Netting Adjustment [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	$ 2,437	$ 2,609