Derivative Financial Instruments (Details 5) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013 counterparties	Dec. 31, 2012 counterparties
Derivative Financial Instruments
Cash and securities pledged as collateral by counterparties	$ 8
Cash and securities pledged as collateral to counterparties	22
Collateral posted under MNAs, credit-risk-contingent provisions in a liability position	9	25
Collateral posted under MNAs for contracts without credit-risk-contingent liabilities	13
Credit Derivatives
Number of counter-parties	9	10
Notional amount	2,102	6,893
Credit exposure	11	33
Exposure, net of collateral	6	5
Gross liability fair value of contracts containing credit-risk-contingent features	22	65
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(12)	(31)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(9)	(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	2
Notional amount	887	29
Credit exposure	2	1
Exposure, net of collateral	2	1
A
Credit Derivatives
Number of counter-parties	4	4
Notional amount	123	2,450
Credit exposure	3	13
Exposure, net of collateral	1	2
A-
Credit Derivatives
Number of counter-parties	3	3
Notional amount	283	797
Credit exposure	2	8
Exposure, net of collateral	2	2
BBB+
Credit Derivatives
Number of counter-parties	1	1
Notional amount	809	3,617
Credit exposure	4	11
Exposure, net of collateral	$ 1