Derivative Financial Instruments and Off-balance sheet Financial Instruments (Details 5) $ in Millions	Dec. 31, 2016 USD ($) counter-party	Dec. 31, 2015 USD ($) counter-party
Derivative Financial Instruments and Off-balance sheet Financial Instruments
Cash and securities pledged as collateral by counterparties	$ 13
Securities pledged as collateral to counterparties	27
Collateral posted under MNAs, credit-risk-contingent provisions in a liability position	$ 0	$ (13)
Credit Derivatives
Number of counter-parties | counter-party	8	9
Notional amount	$ 888	$ 547
Credit exposure	23	17
Exposure, net of collateral	12	7
Gross liability fair value of contracts containing credit-risk-contingent features	9	21
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(7)	(3)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	0	(13)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	$ 2	$ 5
AA–
Credit Derivatives
Number of counter-parties | counter-party	2	0
Notional amount	$ 80	$ 0
Credit exposure	2	0
Exposure, net of collateral	$ 2	$ 0
A plus
Credit Derivatives
Number of counter-parties | counter-party	5	1
Notional amount	$ 698	$ 82
Credit exposure	20	5
Exposure, net of collateral	$ 9	$ 0
A
Credit Derivatives
Number of counter-parties | counter-party	0	5
Notional amount	$ 0	$ 375
Credit exposure	0	9
Exposure, net of collateral	$ 0	$ 6
A-
Credit Derivatives
Number of counter-parties | counter-party	1	1
Notional amount	$ 110	$ 41
Credit exposure	1	3
Exposure, net of collateral	$ 1	$ 0
BBB+
Credit Derivatives
Number of counter-parties | counter-party	0	2
Notional amount	$ 0	$ 49
Credit exposure	0	0
Exposure, net of collateral	$ 0	$ 1