Fair Value Measurements Fair Value Measurements (Details Textual) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 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	$ (4)	$ 4	$ 9	$ 29
Credit standing adjustment assumption net of reinsurance [Member]
Derivative [Line Items]
Pre-tax realized gains	$ 16	$ 1	$ (33)	$ 0