Derivative Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	Jun. 30, 2011	Dec. 31, 2010
Derivative Financial Instruments
Cash and securities pledged as collateral by counterparties	$ 83
Securities pledged as collateral to counterparties	107
Collateral posted under MNAs, credit-risk-contingent provisions in a liability position	48	171
Collateral posted under MNAs for contracts without credit-risk-contingent liabilities	59
Credit Derivatives
Number of counter-parties	9	11
Notional amount	9,873	9,079
Credit exposure	129	107
Exposure, net of collateral	47	74
Gross liability fair value of contracts containing credit-risk-contingent features	146	448
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(90)	(255)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(48)	(171)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	8	22
AA-
Credit Derivatives
Number of counter-parties	1	2
Notional amount	567	2,322
Credit exposure	16	43
Exposure, net of collateral		16
A+
Credit Derivatives
Number of counter-parties	3	5
Notional amount	5,140	3,189
Credit exposure	28	16
Exposure, net of collateral	8	10
A
Credit Derivatives
Number of counter-parties	4	3
Notional amount	4,161	3,479
Credit exposure	50	17
Exposure, net of collateral	4	17
A-
Credit Derivatives
Number of counter-parties		1
Notional amount		89
Credit exposure		31
Exposure, net of collateral		31
BBB+
Credit Derivatives
Number of counter-parties	1
Notional amount	5
Credit exposure	35
Exposure, net of collateral	$ 35