Derivative Financial Instruments (Details 4) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011 contract counterparties entity	Dec. 31, 2010 contract counterparties
Derivative Financial Instruments
Cash and securities pledged as collateral by counterparties	$ 67
Securities pledged as collateral to counterparties	125
Collateral posted under MNAs, credit-risk-contingent provisions in a liability position	110	171
Collateral posted under MNAs for contracts without credit-risk-contingent liabilities	15
Credit Derivatives
Number of counter-parties	13	11
Notional amount	11,190	9,079
Credit exposure	125	107
Exposure, net of collateral	58	74
Gross liability fair value of contracts containing credit-risk-contingent features	248	448
Gross asset fair value of contracts containing credit-risk-contingent features and subject to MNAs	(131)	(255)
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(110)	(171)
Maximum amount of additional exposure for contracts with credit-risk-contingent features if all features were triggered concurrently	7	22
AA
Credit Derivatives
Number of counter-parties	1
Notional amount	25
Credit exposure	1
Exposure, net of collateral	1
AA-
Credit Derivatives
Number of counter-parties	3	2
Notional amount	4,030	2,322
Credit exposure	38	43
Exposure, net of collateral	6	16
A+
Credit Derivatives
Number of counter-parties	4	5
Notional amount	5,056	3,189
Credit exposure	18	16
Exposure, net of collateral	6	10
A
Credit Derivatives
Number of counter-parties	3	3
Notional amount	2,022	3,479
Credit exposure	28	17
Exposure, net of collateral	5	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	2
Notional amount	57
Credit exposure	40
Exposure, net of collateral	$ 40