Derivative Financial Instruments (Details 5) $ in Millions	9 Months Ended
	Sep. 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	$ 4,659	$ 3,776
The number of reference entities generally included in a CDX index | entity	125
Credit default contracts
Credit Derivatives
Notional amount	$ 105	245
Fair value	1	(1)
Credit default contracts | Single name | Corporate debt
Credit Derivatives
Notional amount	25	65
Fair value	0	1
Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount		100
Fair value		(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	21
AA | Credit default contracts | Single name | Corporate debt
Credit Derivatives
Notional amount	0	20
AA | Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount		0
AA | Credit default contracts | Index | Corporate debt
Credit Derivatives
Notional amount	1	1
A | Credit default contracts
Credit Derivatives
Notional amount	19	29
A | Credit default contracts | Single name | Corporate debt
Credit Derivatives
Notional amount	0	10
A | Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount		0
A | Credit default contracts | Index | Corporate debt
Credit Derivatives
Notional amount	19	19
BBB | Credit default contracts
Credit Derivatives
Notional amount	66	185
BBB | Credit default contracts | Single name | Corporate debt
Credit Derivatives
Notional amount	20	35
BBB | Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount		100
BBB | Credit default contracts | Index | Corporate debt
Credit Derivatives
Notional amount	46	50
BB and lower | Credit default contracts
Credit Derivatives
Notional amount	19	10
BB and lower | Credit default contracts | Single name | Corporate debt
Credit Derivatives
Notional amount	5	0
BB and lower | Credit default contracts | First-to-default Basket | Municipal
Credit Derivatives
Notional amount		0
BB and lower | Credit default contracts | Index | Corporate debt
Credit Derivatives
Notional amount	$ 14	$ 10