Fair Value of Financial Instruments Fair Value of Financial Instruments - Quantitative Estimates for Level 3 Liabilities (Details) - Level 3 - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, liabilities	$ 175.4	$ 160.3
Embedded derivatives
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, liabilities	175.4	160.3
Embedded derivatives | Budget method | Fixed Annuity
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, liabilities	$ 172.3	$ 153.9
CSA	3.32%	3.08%
Embedded derivatives | Budget method | Fixed Annuity | Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Swap curve	0.31%	0.24%
Mortality rate	97.00%	97.00%
Lapse rate	0.04%	0.04%
Embedded derivatives | Budget method | Fixed Annuity | Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Swap curve	2.80%	2.55%
Mortality rate	105.00%	105.00%
Lapse rate	46.44%	46.44%
Embedded derivatives | Risk neutral stochastic valuation methodology | GMAB / GMWB / COMBO
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, liabilities	$ 3.1	$ 6.4
Mortality rate	105.00%	105.00%
CSA	3.32%	3.08%
Embedded derivatives | Risk neutral stochastic valuation methodology | GMAB / GMWB / COMBO | Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Swap curve	0.25%	0.21%
Lapse rate	0.00%	0.00%
Volatility surface	8.16%	9.89%
Embedded derivatives | Risk neutral stochastic valuation methodology | GMAB / GMWB / COMBO | Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Swap curve	3.02%	2.76%
Lapse rate	40.00%	40.00%
Volatility surface	61.32%	67.34%