Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended									0 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Federal Home Loan Bank Borrowings Line of Credit	Dec. 31, 2013 Federal Home Loan Bank Borrowings Line of Credit	Mar. 31, 2014 Federal Home Loan Bank Borrowings Letter of Credit	Dec. 31, 2013 Federal Home Loan Bank Borrowings Letter of Credit	Mar. 31, 2014 Investment purchase commitment	Dec. 31, 2013 Investment purchase commitment	Mar. 31, 2014 Investment purchase commitment Consolidated investment entities	Dec. 31, 2013 Investment purchase commitment Consolidated investment entities	Sep. 26, 2012 Healthcare Strategies, Inc., Plan plaintiff	Apr. 11, 2014 Subsequent Event Healthcare Strategies, Inc., Plan
Loss Contingencies [Line Items]
Off-balance sheet commitment to purchase investments							$ 1,100.0	$ 1,200.0	$ 323.2	$ 321.3
Undiscounted liability of future guaranty fund assessments	26.9	19.2
Future credits to premium taxes	26.5	18.4
Amount of borrowing capacity			1,800.0	1,800.0	255.0	265.0
Fair value of assets pledged as collateral			2,100.0	2,000.0	301.2	294.1
Possible losses in excess of amounts accrued	100.0
Number of plaintiffs											15,000
Damages sought by plaintiffs												$ 15.0