Closed Block (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Closed Block liabilities
Closed Block liabilities: Future policy benefits and claims	$ 4,366.5	$ 4,532.0
Closed Block liabilities: Other policyholder funds	9.6	10.5
Closed Block liabilities: Policyholder dividends payable	259.2	270.5
Closed Block liabilities: Policyholder dividend obligation	165.2	111.6
Closed Block liabilities: Deferred income taxes		2.2
Closed Block liabilities: Other liabilities	17.6	24.7
Total Closed Block liabilities	4,818.1	4,951.5
Assets designated to the Closed Block
Closed Block assets: Fixed maturities, available-for-sale	2,399.5	2,470.9
Closed Block assets: Fixed maturities, trading	11.9	13.4
Closed Block assets: Equity securities, available-for-sale	3.8	3.6
Closed Block assets: Mortgage loans	912.1	828.6
Closed Block assets: Policy loans	610.0	644.2
Closed Block assets: Other investments	101.1	118.5
Closed Block assets: Total investments	4,038.4	4,079.2
Closed Block assets: Cash and cash equivalents	29.2	70.3
Closed Block assets: Accrued investment income	48.8	49.5
Closed Block assets: Premiums due and other receivables	13.6	11.7
Closed Block assets: Deferred income tax asset	58.1	66.2
Closed Block assets: Other assets		2.2
Total assets designated to the Closed Block	4,188.1	4,279.1
Excess of Closed Block liabilities over assets designated to the Closed Block	630.0	672.4
Amounts included in accumulated other comprehensive income (loss)	18.9	12.9
Maximum future earnings to be recognized from Closed Block assets and liabilities	$ 648.9	$ 685.3	$ 723.8	$ 787.0