Separate Accounts, Death Benefits and Other Insurance Benefit Features and Embedded Product Derivatives - Changes in Guaranteed Insurance Benefit Liability Balances (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Variable Annuity GMDB
Movement in Guaranteed Benefit Liability, Gross [Roll Forward]
Balance, beginning of period	$ 16.3	$ 17.0
Incurred	(0.4)	(0.1)
Paid	(0.3)	(0.3)
Assumption unlocking	0.3	0
Change due to net unrealized gains or losses included in AOCI	0.1	0
Balance, end of period	16.0	16.6
Variable Annuity GMIB
Movement in Guaranteed Benefit Liability, Gross [Roll Forward]
Balance, beginning of period	16.4	9.5
Incurred	(2.4)	(0.2)
Paid	0	0
Assumption unlocking	0	0
Change due to net unrealized gains or losses included in AOCI	0	(0.1)
Balance, end of period	14.0	9.2
Fixed Indexed Annuity GMWB & GMDB
Movement in Guaranteed Benefit Liability, Gross [Roll Forward]
Balance, beginning of period	147.0	85.4
Incurred	(10.5)	(0.4)
Paid	(0.1)	(0.1)
Assumption unlocking	0	0
Change due to net unrealized gains or losses included in AOCI	13.9	18.5
Balance, end of period	171.3	104.2
Universal Life Secondary Guarantees
Movement in Guaranteed Benefit Liability, Gross [Roll Forward]
Balance, beginning of period	166.3	145.8
Incurred	(9.3)	(7.8)
Paid	(6.4)	(1.9)
Assumption unlocking	0	0
Change due to net unrealized gains or losses included in AOCI	1.2	0.8
Balance, end of period	$ 170.4	$ 152.5