Income Tax Matters, Reconciliation Between Income Tax Provision and Statutory Income Tax Provision Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation between income tax provision and statutory income tax provision:
Amount of federal income tax (provision) benefit based on the statutory rate	$ (46.5)	$ (51.5)	$ 130.1
(Increase) decrease in federal valuation allowances	0.5	(0.3)	(0.6)
Non-deductible compensation (expense) benefit	(2.3)	0.3	(0.2)
Non-deductible (expense)	0.0	(0.3)	(0.3)
State income taxes, net of federal benefit	(4.3)	(4.2)	4.2
Foreign income tax (expense) benefit	(0.1)	0.5	0.1
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	(5.9)	0.0	0.0
Expiration of statute of limitations	0.0	0.0	1.7
Effective Income Tax Rate Reconciliation, Tax Settlement, Foreign, Amount	29.0	0.0	0.0
Advance pricing agreement	0.0	0.0	(0.2)
Competent Authority settlement	0.0	0.0	0.4
Income tax (provision) benefit	(87.6)	(55.5)	135.2
State and Local Jurisdiction [Member]
Reconciliation between income tax provision and statutory income tax provision:
(Increase) decrease in federal valuation allowances	2.2	(0.3)
State and tax expense (benefit) before adjustments	4.0	4.1	(10.3)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ (2.5)	$ 0.2	(3.1)
Increase (decrease) in state income tax expense (benefit) due to expiring net operating losses			$ (3.0)