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					12 Months Ended		3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013 Variable Annuity GMDB	Mar. 31, 2012 Variable Annuity GMDB	Mar. 31, 2013 Variable Annuity GMIB	Mar. 31, 2012 Variable Annuity GMIB	Mar. 31, 2013 Fixed Indexed Annuity GMWB & GMDB	Dec. 31, 2012 Fixed Indexed Annuity GMWB & GMDB	Mar. 31, 2012 Fixed Indexed Annuity GMWB & GMDB	Mar. 31, 2013 Universal Life Secondary Guarantees	Dec. 31, 2012 Universal Life Secondary Guarantees	Mar. 31, 2012 Universal Life Secondary Guarantees	Mar. 31, 2013 Universal Life	Dec. 31, 2012 Universal Life	Mar. 31, 2013 Universal Life	Dec. 31, 2012 Universal Life
Movement in Guaranteed Benefit Liability, Gross [Roll Forward]
Additional liability balance, beginning of the period													$ 300.4	$ 203.0
Expense													13.8	37.1
Liability balance, beginning of the period	10.8	10.8	20.9	17.0	103.6	5.6	103.6	115.8	100.6	115.8
Incurred	0.4	1.0	1.2	3.8	12.6	40.1		15.2	22.6
Paid	(0.7)	(1.0)	0	0	(0.1)	0		(3.4)	(9.5)
Change due to net unrealized gains or losses included in AOCI	0.1	0	(0.1)	0.3	1.4	57.9					0.4	2.1	10.6	16.9
Assumption unlocking	0	0	0	(0.2)	0	0		0	0				0	43.4
Liability balance, end of the period	10.6		22.0		117.5	103.6	103.6	128.0	115.8	115.8
Additional liability balance, end of the period													$ 324.8	$ 300.4