Derivative Financial Instruments (Details 5) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013 counterparties	Dec. 31, 2012 counterparties
Derivative Financial Instruments
Cash and securities pledged as collateral by counterparties	$ 14
Cash and securities pledged as collateral to counterparties	24
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	11
Credit Derivatives
Number of counter-parties	10	10
Notional amount	1,423	6,893
Credit exposure	18	33
Exposure, net of collateral	6	5
Gross liability fair value of contracts containing credit-risk-contingent features	29	65
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(14)	(31)
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	2	9
A+
Credit Derivatives
Number of counter-parties	2	2
Notional amount	101	29
Credit exposure	1	1
Exposure, net of collateral	1	1
A
Credit Derivatives
Number of counter-parties	3	4
Notional amount	32	2,450
Credit exposure	2	13
Exposure, net of collateral		2
A-
Credit Derivatives
Number of counter-parties	4	3
Notional amount	514	797
Credit exposure	11	8
Exposure, net of collateral	4	2
BBB+
Credit Derivatives
Number of counter-parties	1	1
Notional amount	776	3,617
Credit exposure	4	11
Exposure, net of collateral	$ 1