Derivative Financial Instruments (Credit Derivatives-Selling Protection) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) entity	Dec. 31, 2015 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Term of credit default swaps (in years)	5 years
Credit Derivatives
Notional amount	$ 3,188	$ 3,259
The number of reference entities generally included in a CDX index | entity	125
Credit default contracts
Credit Derivatives
Notional amount	$ 180	180
Fair value	(3)	(7)
Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount	100	100
Fair value	(4)	(8)
Credit default contracts | Index | Corporate debt
Credit Derivatives
Notional amount	80	80
Fair value	1	1
AA | Credit default contracts
Credit Derivatives
Notional amount	1	1
AA | Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount	0	0
AA | Credit default contracts | Index | Corporate debt
Credit Derivatives
Notional amount	1	1
A | Credit default contracts
Credit Derivatives
Notional amount	19	20
A | Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount	0	0
A | Credit default contracts | Index | Corporate debt
Credit Derivatives
Notional amount	19	20
BBB | Credit default contracts
Credit Derivatives
Notional amount	149	152
BBB | Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount	100	100
BBB | Credit default contracts | Index | Corporate debt
Credit Derivatives
Notional amount	49	52
BB and lower | Credit default contracts
Credit Derivatives
Notional amount	11	7
BB and lower | Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount	0	0
BB and lower | Credit default contracts | Index | Corporate debt
Credit Derivatives
Notional amount	$ 11	$ 7