Derivative Financial Instruments (Narrative) (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) NumberOfDerivativeContracts	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Derivative [Line Items]
S & P 500 index options purchased per month | NumberOfDerivativeContracts			2
Expiry date of S & P 500 index options purchased, years			1 year
Derivative Option premiums paid	$ 2.0	$ 2.2	$ 6.2	$ 6.3
Amount received for derivative options exercised	2.9	4.7	$ 11.3	14.6
Maximum credit exposure required increase in S&P 500 index, percentage			15.30%
Impact On Interest Credited Changes In Actuarial Assumptions	(1.5)	$ (1.4)	$ 2.2	$ (2.7)
Cash Collateral	19.8		19.8		$ 12.2
Fixed Maturity Securities Collateral	13.9		13.9		$ 0.0
Cash Flow Hedging [Member]
Derivative [Line Items]
Amounts in Gains (Losses) Deferred in AOCI on Derivatives			5.3
Purchase of Fixed Maturity Securities, Par Value			115.0
Gain (Loss) to be reclassed to earnings over next 12 months			$ (0.4)
Weighted-Average Years deferred losses in AOCI will be relcassifed to Earnings			P26Y0M0D
Deferred Loss on Fixed Maturity Securites			$ 9.6
Derivative Amount	$ 252.9		$ 252.9
Weighted-Average Fixed Rate	5.13%		5.13%
Derivative Maturity			Jun. 01, 2042
Derivative Contract Inception Date			Jun. 01, 2017