Separate Accounts, Death Benefits and Other Insurance Benefit Features and Embedded Product Derivatives - Changes in Liability Balances (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Universal Life
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Balance, beginning of period	$ 366.6	$ 270.3
Incurred	12.1	16.4
Assumption unlocking	(4.6)	0
Change due to net unrealized gains or losses included in AOCI	23.5	13.6
Balance, end of period	397.6	300.3
Fixed Indexed Annuity GMWB & GMDB
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
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
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
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