Fair Value Measurements Fair Value Measurements (Details Textual) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Maximum [Member]
Derivative [Line Items]
Daily analyses identify price			5.00%
Minimum [Member]
Derivative [Line Items]
Daily analyses identify price			3.00%
Percentage difference of sale trade price from prior days price			3.00%
Percentage difference of purchase trade price from current days price			3.00%
Percentage difference of weekly analyses identify price from published bond			5.00%
Percentage change of monthly analyses identify price			3.00%
Outperformance (underperformance) of the underlying actively managed fund compared to indices [Member]
Derivative [Line Items]
Pre-tax realized gains	$ 25	$ (131)	$ 34	$ (102)
Credit standing adjustment assumption net of reinsurance [Member]
Derivative [Line Items]
Pre-tax realized gains	(31)	75	(64)	75
Policyholder Behavior Assumptions [Member]
Derivative [Line Items]
Pre-tax realized gains	$ 0	$ 0	$ 301	$ 51