Investments and Derivative Instruments (Details 19) (Credit [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Corporate Credit/Foreign Gov. [Member] | Single Name Credit Default Swaps [Member] | Investment Grade Risk Exposure [Member]
Derivative [Line Items]
Notional Amount	$ 1,586		$ 1,787
Fair Value	14		8
Weighted Average Years to Maturity	3 years	3 years
Underlying Referenced Credit Obligation Type	Corporate Credit/ Foreign Gov.	Corporate Credit/ Foreign Gov.
Average Credit Rating	A	A
Offsetting Notional Amount	778		878
Offsetting Fair Value	(14)		(19)
Corporate Credit [Member] | Single Name Credit Default Swaps [Member] | Below Investment Grade Risk Exposure [Member]
Derivative [Line Items]
Notional Amount	101		114
Fair Value	0		(1)
Weighted Average Years to Maturity	1 year	1 year
Underlying Referenced Credit Obligation Type	Corporate Credit	Corporate Credit
Average Credit Rating	B	B+
Offsetting Notional Amount	101		114
Offsetting Fair Value	(2)		(3)
Corporate Credit [Member] | Basket Credit Default Swaps [Member] | Investment Grade Risk Exposure [Member]
Derivative [Line Items]
Notional Amount	2,013		2,074
Fair Value	12		11
Weighted Average Years to Maturity	2 years	2 years
Underlying Referenced Credit Obligation Type	Corporate Credit	Corporate Credit
Average Credit Rating	BBB+	BBB+
Offsetting Notional Amount	1,234		1,326
Offsetting Fair Value	(6)		(6)
Corporate Credit [Member] | Basket Credit Default Swaps [Member] | Below Investment Grade Risk Exposure [Member]
Derivative [Line Items]
Notional Amount			115
Fair Value			(27)
Weighted Average Years to Maturity		4 years
Underlying Referenced Credit Obligation Type		CMBS Credit
Average Credit Rating		B+
Offsetting Notional Amount			115
Offsetting Fair Value			27
Corporate Credit [Member] | Embedded Credit Derivatives [Member] | Investment Grade Risk Exposure [Member]
Derivative [Line Items]
Notional Amount	150		325
Fair Value	139		296
Weighted Average Years to Maturity	4 years	4 years
Underlying Referenced Credit Obligation Type	Corporate Credit	Corporate Credit
Average Credit Rating	BBB	BBB-
Offsetting Notional Amount	0		0
Offsetting Fair Value	0		0
CMBS Credit [Member] | Basket Credit Default Swaps [Member] | Investment Grade Risk Exposure [Member]
Derivative [Line Items]
Notional Amount	237		237
Fair Value	(10)		(12)
Weighted Average Years to Maturity	4 years	4 years
Underlying Referenced Credit Obligation Type	CMBS Credit	CMBS Credit
Average Credit Rating	A	A
Offsetting Notional Amount	238		238
Offsetting Fair Value	10		12
CMBS Credit [Member] | Basket Credit Default Swaps [Member] | Below Investment Grade Risk Exposure [Member]
Derivative [Line Items]
Notional Amount	115
Fair Value	(24)
Weighted Average Years to Maturity	4 years
Underlying Referenced Credit Obligation Type	CMBS Credit
Average Credit Rating	B
Offsetting Notional Amount	115
Offsetting Fair Value	$ 24