Income Taxes - Statutory Federal Income Tax Expense, Effective Income Tax Expense, Rates (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Statutory Federal Income Tax Expense									$ (56.1)	$ (110.0)	$ (42.8)
Statutory Federal Income Tax Expense, Rate, percentage									35.00%	35.00%	35.00%
Tax-exempt Income and Dividends Received Deduction									9.0	10.6	13.9
Tax-exempt Income and Dividends Received Deduction, Rate, percentage									(5.60%)	(3.40%)	(11.40%)
State Income Taxes									(0.6)	(0.2)	(0.8)
State Income Taxes, Rate, percentage									0.40%	0.10%	0.70%
Other, Net									0.1	(0.3)	(0.9)
Other, Net, Rate, percentage									(0.10%)	0.10%	0.70%
Income Tax Expense	$ (29.8)	$ 0.8	$ (1.9)	$ (16.7)	$ (26.6)	$ (33.4)	$ (13.9)	$ (26.0)	$ (47.6)	$ (99.9)	$ (30.6)
Effective Income Tax Expense, Rate, percentage									29.70%	31.80%	25.00%