Variable Interest Entities - Credit Related Note, Asset Swap Vehicle VIEs (Details 2b) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Variable Interest Entity, Not Primary Beneficiary
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	$ 1,000,000,000	$ 1,500,000,000
Par value of collateral held by VIEs	20,600,000,000	20,800,000,000
Variable Interest Entity, Not Primary Beneficiary | Credit linked notes
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	500,000,000	1,100,000,000
Par value of collateral held by VIEs	12,000,000,000	12,900,000,000
Variable Interest Entity, Not Primary Beneficiary | Static structure
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	0	500,000,000
Par value of collateral held by VIEs	6,500,000,000	7,300,000,000
Variable Interest Entity, Not Primary Beneficiary | Managed structure
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	500,000,000	600,000,000
Par value of collateral held by VIEs	5,500,000,000	5,600,000,000
Variable Interest Entity, Not Primary Beneficiary | Asset Swap VIEs
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	500,000,000	400,000,000
Par value of collateral held by VIEs	8,600,000,000	7,900,000,000
Variable Interest Entity, Primary Beneficiary | Credit linked notes
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Variable Interest Entity, Consolidated, Carrying Amount, Assets	435,000,000	483,000,000
Net derivative receivables | Variable Interest Entity, Not Primary Beneficiary
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	1,000,000,000	1,500,000,000
Net derivative receivables | Variable Interest Entity, Not Primary Beneficiary | Credit linked notes
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	500,000,000	1,100,000,000
Net derivative receivables | Variable Interest Entity, Not Primary Beneficiary | Static structure
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	0	500,000,000
Net derivative receivables | Variable Interest Entity, Not Primary Beneficiary | Managed structure
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	500,000,000	600,000,000
Net derivative receivables | Variable Interest Entity, Not Primary Beneficiary | Asset Swap VIEs
Exposure to nonconsolidated credit-linked note and asset swap VIEs [Abstract]
Exposure to non-consolidated VIEs	$ 500,000,000	$ 400,000,000