Derivative Financial Instruments (Details 4) $ in Millions	Sep. 30, 2017 USD ($) counter-party	Dec. 31, 2016 USD ($) counter-party
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash and securities pledged as collateral by counterparties	$ 3
Securities pledged as collateral to counterparties	18
Collateral posted under MNAs for contracts containing credit-risk-contingent features	7	$ 0
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	$ 11
Credit Derivatives
Number of counter- parties | counter-party	4	8
Notional amount	$ 260	$ 888
Credit exposure	4	23
Exposure, net of collateral	4	12
Gross liability fair value of contracts containing credit-risk-contingent features	20	9
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(8)	(7)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	$ 5	$ 2
AA-
Credit Derivatives
Number of counter- parties | counter-party	1	2
Notional amount	$ 11	$ 80
Credit exposure	0	2
Exposure, net of collateral	$ 0	$ 2
A plus
Credit Derivatives
Number of counter- parties | counter-party	3	5
Notional amount	$ 249	$ 698
Credit exposure	4	20
Exposure, net of collateral	$ 4	$ 9
A-
Credit Derivatives
Number of counter- parties | counter-party	0	1
Notional amount	$ 0	$ 110
Credit exposure	0	1
Exposure, net of collateral	$ 0	$ 1