Income Tax Matters, Reconciliation Between Income Tax Provision and Statutory Income Tax Provision Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation between income tax provision and statutory income tax provision:
Amount of federal income tax benefit (provision) based on the statutory rate	$ 130.1	$ (37.5)	$ (50.1)
(Increase) decrease in federal valuation allowances	(0.6)	0.0	0.1
Non-deductible compensation expense	(0.2)	(0.1)	(0.3)
Non-deductible expense	(0.3)	(0.3)	(0.9)
State income taxes, net of federal benefit	4.2	0.0	(4.4)
Foreign income tax benefit	0.1	0.3	0.0
Expiration of statute of limitations	1.7	2.3	4.6
Settlement with taxing authorities	0.0	0.0	4.4
Advance pricing agreement	(0.2)	0.0	2.9
Competent Authority settlement	0.4	0.0	5.3
Income tax benefit (provision)	135.2	(35.3)	(38.4)
State and tax expense (benefit) before adjustments	(10.3)	2.3	4.4
Increase (decrease) in state tax expense (benefit) due to change in tax rate	3.1	$ (1.6)
Increase (decrease) in state income tax expense (benefit) due to expiring net operating losses	$ 3.0
Increase (decrease) in state tax expense (benefit) due to change in valuation allowance			$ 1.2