Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 years	Dec. 31, 2010
Fair Value Measurements [Line Items]
GLB - Lapse rate - lower range	1.00%
GLB - Lapse rate - upper range	6.00%
GLB - Spike lapse rate - lower range	10.00%
GLB - Spike lapse rate - upper range	30.00%
GLB - Ultimate lapse rate	10.00%
GLB - Length of ultimate lapse rate period, years	2
GLB - Adjustment factor for valuable guarantees - lower	15.00%
GLB - Adjustment factor for valuable guarantees - upper	75.00%
GLB - Maximum annuitization rate	8.00%
GLB - Maximum annuitization rate in the first year a policy can annuitize utilizing the GMIB	13.00%
GLB - Weighted average maximum annuitization rate - rate 1	8.00%
GLB - Weighted average maximum annuitization rate - rate 2	12.00%
GLB - Weighted average maximum annuitization rate - rate 3	30.00%
GLB - Number of different annuitization functions used	3
Minimum number of pricing services used to obtain fair value measurements for the majority of the investment securities held	1
The maximum maturity period in years to be classified as a short-term investment	1
Impact of GMIB valuation model changes on net income	$ 14.0	$ 98.0
Redemption Notice Periods Lower Range [Member]
Fair Value Measurements [Line Items]
Notice period for redemption for alternative investments investment funds, days	5
Redemption Notice Periods Upper Range [Member]
Fair Value Measurements [Line Items]
Notice period for redemption for alternative investments investment funds, days	120