Contingencies, Commitments and Guarantees (Details 1) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012
Loss Contingencies [Line Items]
Receivable for reimbursement of paid assessments	$ 22,481		$ 21,634
Other Assets:
Premium tax offset for future undiscounted assessments	114	97
Premium tax offsets currently available for paid assessments	14	14
Other Liabilities:
Insolvency assessments	205	193
Insurance-related Assessments [Member]
Loss Contingencies [Line Items]
Receivable for reimbursement of paid assessments			6
Total assets held for insolvency assessments	134	117	134
Loss contingency, estimate of possible loss	$ 40.0		$ 40.0