Derivative Financial Instruments (Details 5) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013 party	Dec. 31, 2012 party
Derivative Financial Instruments
Cash and securities pledged as collateral by counterparties	$ 7
Securities pledged as collateral to counterparties	23
Collateral posted under MNAs, credit-risk-contingent provisions in a liability position	13	25
Collateral posted under MNAs for contracts without credit-risk-contingent liabilities	10
Credit Derivatives
Number of counter-parties	8	7
Notional amount	964	6,199
Credit exposure	7	24
Exposure, net of collateral	2	1
Gross liability fair value of contracts containing credit-risk-contingent features	26	62
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(12)	(28)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(13)	(25)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	1	9
A+
Credit Derivatives
Number of counter-parties	1	1
Notional amount	21	19
A
Credit Derivatives
Number of counter-parties	3	3
Notional amount	32	2,252
Credit exposure	2	12
A-
Credit Derivatives
Number of counter-parties	3	2
Notional amount	135	311
Credit exposure	1	1
Exposure, net of collateral	1	1
BBB+
Credit Derivatives
Number of counter-parties	1	1
Notional amount	776	3,617
Credit exposure	4	11
Exposure, net of collateral	$ 1