Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	35.00%
Effective tax rate	(90.80%)	(22.90%)	(2.10%)
Total income tax expense (benefit)	$ 17.6
Tax benefit from the reduction in net deferred tax liabilities	17.6
DRD constituting non-taxable investment income	155.0	$ 142.0	$ 161.0
Non-taxable investment income	$ 157.0	146.0	161.0
Percent of income tax expense (benefit)	5.00%
Income (loss) from domestic operations	$ 170.0	$ 321.0	$ 497.0