Derivative Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015 counter-party	Dec. 31, 2014 counter-party
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash and securities pledged as collateral by counterparties	$ 9
Securities pledged as collateral to counterparties	32
Collateral posted under MNAs, credit-risk-contingent provisions in a liability position	(19)	(7)
Collateral posted under MNAs for contracts without credit-risk-contingent liabilities	13
Credit Derivatives
Number of counter- parties	8	7
Notional amount	455	353
Credit exposure	12	5
Exposure, net of collateral	3	3
Gross liability fair value of contracts containing credit-risk-contingent features	27	16
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(3)	(4)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(19)	(7)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	5	5
A plus
Credit Derivatives
Number of counter- parties	1	1
Notional amount	104	164
Credit exposure	4	2
Exposure, net of collateral	0	1
A
Credit Derivatives
Number of counter- parties	5	3
Notional amount	277	118
Credit exposure	8	3
Exposure, net of collateral	3	2
A-
Credit Derivatives
Number of counter- parties	1	1
Notional amount	24	8
Credit exposure	0	0
Exposure, net of collateral	0	0
BBB+
Credit Derivatives
Number of counter- parties	0	1
Notional amount	0	11
Credit exposure	0	0
Exposure, net of collateral	0	0
BBB
Credit Derivatives
Number of counter- parties	1	1
Notional amount	50	52
Credit exposure	0	0
Exposure, net of collateral	$ 0	$ 0