Contracts Accounted for as Credit Derivatives - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	6 years 2 months	5 years 3 months 6 days
Net par outstanding	$ 12,856	$ 16,997
Collateral agreed to be posted	$ 36	116
Market value collateralized debt obligations of corporate obligations [Member]
Credit Derivatives
Average obligor size (less than)	1.00%
Maximum exposure of one industry (as a percent)	10.00%
Net par outstanding	$ 6,860	10,425
Collateral Debt Obligations, Collateral Requirement [Member]
Credit Derivatives
Amount of par subject to collateral for which the amount of collateral is capped	506
Collateral agreed to be posted		116
Collateral Debt Obligations, Collateral Cap Negotiated [Member]
Credit Derivatives
Amount of par subject to collateral for which the amount of collateral is capped	333	516
Collateral agreed to be posted		100
Collateral posted, based on mark-to-market valuation	27
Collateral Debt Obligations, No Cap Negotiated [Member]
Credit Derivatives
Amount of par subject to collateral for which the amount of collateral is capped	300
Collateral agreed to be posted	36
Collateral posted, based on mark-to-market valuation	9	16
Notional amount subject to collateral based on movements in the mark-to-market valuation of the underlying exposure	$ 173	174
Gross par of contracts expected to be terminated		183
Collateral already posted being terminated		$ 73