Derivative Financial Instruments (Details 5) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($) entity	Dec. 31, 2016 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Term of credit default swaps (in years)	5 years
Credit Derivatives
Notional amount	$ 2,997	$ 2,919
The number of reference entities generally included in a CDX index | entity	125
Credit default contracts
Credit Derivatives
Notional amount	$ 181	180
Fair value	1	(2)
Credit default contracts | Single name | Corporate debt
Credit Derivatives
Notional amount	1
Fair value	0
Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount	100	100
Fair value	0	(3)
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 | Single name | Corporate debt
Credit Derivatives
Notional amount	0
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	17	19
A | Credit default contracts | Single name | Corporate debt
Credit Derivatives
Notional amount	0
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	17	19
BBB | Credit default contracts
Credit Derivatives
Notional amount	149	150
BBB | Credit default contracts | Single name | Corporate debt
Credit Derivatives
Notional amount	0
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	50
BB and lower | Credit default contracts
Credit Derivatives
Notional amount	14	10
BB and lower | Credit default contracts | Single name | Corporate debt
Credit Derivatives
Notional amount	1
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	$ 13	$ 10