Deferred Policy Acquisition Costs and Value of Business Acquired (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance	$ 476.4	$ 520.4
Deferrals of commissions and expenses	20.8	18.3
Amortization:
Amortization	(16.5)	(9.4)
Interest accrued	9.4	9.3
Net amortization included in the Consolidated Statements of Operations	(7.1)	(0.1)
Change due to unrealized capital gains/losses on available-for-sale securities	(14.2)	(88.0)
Ending balance	475.9	450.6
Movement Analysis Of Value of Business Acquired VOBA [Roll Forward]
Beginning balance	537.4	708.7
Deferrals of commissions and expenses	1.2	1.4
Amortization	(6.6)	(11.4)
Interest accrued	11.9	13.5
Net amortization included in the Condensed Consolidated Statements of Operations	5.3	2.1
Change due to unrealized capital gains/losses on available-for-sale securities	(19.1)	(133.5)
Ending balance	524.8	578.7
Movement Analysis of Deferred Policy Acquisition Costs and Value of Business Acquired (VOBA) [Roll Forward]
Beginning balance	1,013.8	1,229.1
Deferrals of commissions and expenses	22.0	19.7
Amortization	(23.1)	(20.8)
Interest accrued	21.3	22.8
Net amortization included in the Condensed Consolidated Statements of Operations	(1.8)	2.0
Change due to unrealized capital gains/losses on available-for-sale securities	(33.3)	(221.5)
Ending balance	1,000.7	1,029.3
DAC/VOBA unlocking	$ 13.7	$ (0.1)
Minimum
Movement Analysis of Deferred Policy Acquisition Costs and Value of Business Acquired (VOBA) [Roll Forward]
Value of Business Acquired (VOBA), Interest accrued percentage	5.50%	5.50%
Maximum
Movement Analysis of Deferred Policy Acquisition Costs and Value of Business Acquired (VOBA) [Roll Forward]
Value of Business Acquired (VOBA), Interest accrued percentage	7.00%	7.00%