Separate Accounts, Death Benefits and Other Insurance Benefit Features and Embedded Product Derivatives - Changes in Guaranteed Insurance Benefit Liability Balances (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Dec. 31, 2014
Guaranteed Minimum Death Benefit | Variable Annuity
Movement in Guaranteed Benefit Liability, Gross [Roll Forward]
Balance, beginning of period	$ 16.0	$ 16.6	$ 16.3	$ 17.0
Incurred	0.5	0.4	0.1	0.3
Paid	(0.8)	(0.7)	(1.1)	(1.0)
Assumption unlocking	0.0	0.0	0.3	0.0
Change due to net unrealized gains or losses included in AOCI	(0.1)	0.0	0.0	0.0
Balance, end of period	15.6	16.3	15.6	16.3
Guaranteed Minimum Income Benefit | Variable Annuity
Movement in Guaranteed Benefit Liability, Gross [Roll Forward]
Balance, beginning of period	14.0	9.2	16.4	9.5
Incurred	0.2	(0.7)	(2.2)	(0.9)
Paid	0.0	0.0	0.0	0.0
Assumption unlocking	0.0	0.0	0.0	0.0
Change due to net unrealized gains or losses included in AOCI	0.0	0.0	0.0	(0.1)
Balance, end of period	14.2	8.5	14.2	16.4
Guaranteed Minimum Withdrawal Benefit And Guaranteed Minimum Death Benefit | Fixed Annuity
Movement in Guaranteed Benefit Liability, Gross [Roll Forward]
Balance, beginning of period	171.3	104.2	147.0	85.4
Incurred	16.0	14.5	26.5	14.9
Paid	(0.1)	(0.1)	(0.2)	(0.2)
Assumption unlocking	0.0	0.0	0.0	0.0
Change due to net unrealized gains or losses included in AOCI	(33.8)	16.5	(19.9)	35.0
Balance, end of period	153.4	135.1	153.4	147.0
Secondary Guarantee | Universal Life
Movement in Guaranteed Benefit Liability, Gross [Roll Forward]
Balance, beginning of period	170.4	152.5	166.3	145.8
Incurred	9.0	8.5	18.3	16.3
Paid	(3.8)	(1.3)	(10.2)	(3.2)
Assumption unlocking	0.0	0.0	0.0	0.0
Change due to net unrealized gains or losses included in AOCI	(2.7)	0.7	(1.5)	1.5
Balance, end of period	$ 172.9	$ 160.4	$ 172.9	$ 166.3