Deferred Policy Acquisition Costs and Value of Business Acquired (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance			$ 476.4	$ 520.4
Deferrals of commissions and expenses			38.9	37.3
Amortization:
Amortization, excluding unlocking			(37.0)	(29.8)
Unlocking			(46.8)	5.6
Interest accrued			19.1	18.8
Net amortization included in the Consolidated Statements of Operations			(64.7)	(5.4)
Change due to unrealized capital gains/losses on available-for-sale securities			(55.7)	(164.5)
Ending balance	$ 394.9	$ 387.8	394.9	387.8
Movement Analysis Of Value of Business Acquired VOBA [Roll Forward]
Beginning balance			537.4	708.7
Deferrals of commissions and expenses			2.5	2.8
Amortization, excluding unlocking			(39.2)	(28.5)
Unlocking			(55.5)	9.9
Interest accrued			23.9	27.2
Net amortization included in the Condensed Consolidated Statements of Operations			(70.8)	8.6
Change due to unrealized capital gains/losses on available-for-sale securities			(70.2)	(247.5)
Ending balance	398.9	472.6	398.9	472.6
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			41.4	40.1
Amortization, excluding unlocking			(76.2)	(58.3)
Unlocking			(102.3)	15.5
Interest accrued			43.0	46.0
Net amortization included in the Condensed Consolidated Statements of Operations	(133.7)	1.2	(135.5)	3.2
Change due to unrealized capital gains/losses on available-for-sale securities			(125.9)	(412.0)
Ending balance	$ 793.8	$ 860.4	$ 793.8	$ 860.4
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%
Guaranteed minimum interest rates
Amortization:
Unlocking			$ (48.3)
Movement Analysis Of Value of Business Acquired VOBA [Roll Forward]
Unlocking			$ (79.7)