Derivative Financial Instruments and Off-balance sheet Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012 party	Dec. 31, 2011 party
Derivative Financial Instruments and Off-balance Sheet Financial Instruments
Cash and securities pledged as collateral by counterparties	$ 23
Securities pledged as collateral to counterparties	25
Credit Derivatives
Number of counter-parties	7	10
Notional amount	6,199	10,746
Credit exposure	24	105
Exposure, net of collateral	1	46
Gross liability fair value of contracts containing credit-risk-contingent features	62	133
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(28)	(60)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(25)	(72)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	9	1
AA-
Credit Derivatives
Number of counter-parties		1
Notional amount		25
Credit exposure		1
Exposure, net of collateral		1
A+
Credit Derivatives
Number of counter-parties	1	3
Notional amount	19	2,936
Credit exposure		24
Exposure, net of collateral		4
A
Credit Derivatives
Number of counter-parties	3	2
Notional amount	2,252	3,913
Credit exposure	12	14
A-
Credit Derivatives
Number of counter-parties	2	2
Notional amount	311	3,815
Credit exposure	1	25
Exposure, net of collateral	1
BBB+
Credit Derivatives
Number of counter-parties	1	2
Notional amount	3,617	57
Credit exposure	11	41
Exposure, net of collateral		$ 41