Variable Interest Entities - Credit Related Note, Asset Swap Vehicle VIEs (Details 2b) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Variable Interest Entity, Not Primary Beneficiary [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	$ 1,500,000,000	$ 4,300,000,000
Par value of collateral held by VIEs	20,800,000,000	25,400,000,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Credit linked notes [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	1,100,000,000	3,700,000,000
Par value of collateral held by VIEs	12,900,000,000	16,800,000,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Static structure [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	500,000,000	1,000,000,000
Par value of collateral held by VIEs	7,300,000,000	9,100,000,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Managed structure [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	600,000,000	2,700,000,000
Par value of collateral held by VIEs	5,600,000,000	7,700,000,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Asset Swap VIEs [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	400,000,000	600,000,000
Par value of collateral held by VIEs	7,900,000,000	8,600,000,000
Variable Interest Entity, Primary Beneficiary [Member] | Credit linked notes [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	483,000,000	231,000,000
Net derivative receivables [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	1,500,000,000	4,300,000,000
Net derivative receivables [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Credit linked notes [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	1,100,000,000	3,700,000,000
Net derivative receivables [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Static structure [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	500,000,000	1,000,000,000
Net derivative receivables [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Managed structure [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	600,000,000	2,700,000,000
Net derivative receivables [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Asset Swap VIEs [Member]
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	$ 400,000,000	$ 600,000,000