Derivatives (Level 3 Derivative Instruments) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Variable annuity benefit guarantee liabilities
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	672.4
Variable annuity benefit guarantee liabilities | Discounted cash flows | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.10%
Mortality (as a percent)	0.00%
Foreign exchange volatilities (as a percent)	10.80%
Index volatilities (as a percent)	13.10%
Variable annuity benefit guarantee liabilities | Discounted cash flows | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	3.00%
Mortality (as a percent)	6.40%
Foreign exchange volatilities (as a percent)	17.40%
Index volatilities (as a percent)	23.90%
Variable annuity benefit guarantee liabilities | Discounted cash flows | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.40%
Mortality (as a percent)	0.90%
Foreign exchange volatilities (as a percent)	12.80%
Index volatilities (as a percent)	19.50%
Foreign exchange and equity index options
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	213.0
Foreign exchange and equity index options | Black-Scholes option pricing model | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	10.80%
Expected equity dividends (as a percent)	1.90%
Index volatilities (as a percent)	13.10%
Foreign exchange and equity index options | Black-Scholes option pricing model | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	17.40%
Expected equity dividends (as a percent)	5.20%
Index volatilities (as a percent)	23.90%
Foreign exchange and equity index options | Black-Scholes option pricing model | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	12.80%
Expected equity dividends (as a percent)	3.10%
Index volatilities (as a percent)	19.50%