Debt - Interest Paid on Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Interest Paid	$ 44.1	$ 45.7	$ 37.7
Senior Notes [Member] | Senior Notes, 6% Due November 30, 2015 [Member]
Debt Instrument [Line Items]
Interest Paid	4.8	15.0	15.0
Senior Notes [Member] | Senior Notes, 6% Due May 15, 2017 [Member]
Debt Instrument [Line Items]
Interest Paid	21.6	21.6	21.6
Senior Notes [Member] | Senior Notes, 4.35 Percent Due February 15, 2025 [Member]
Debt Instrument [Line Items]
Interest Paid	5.2	0.0	0.0
Subordinated Debt [Member] | Subordinated Debenture, 7.375 Percent Due 2054 [Member]
Debt Instrument [Line Items]
Interest Paid	11.1	8.5	0.0
Mortgage Note Payable [Member]
Debt Instrument [Line Items]
Interest Paid	0.0	0.0	0.3
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Interest Paid	1.4	0.6	0.8
Federal Home Loan Bank of Chicago [Member]
Debt Instrument [Line Items]
Interest Paid	0.0	0.0	0.0
Federal Home Loan Bank of Dallas [Member]
Debt Instrument [Line Items]
Interest Paid	$ 0.0	$ 0.0	$ 0.0