Income Taxes - Net Operating Losses and Tax Rates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net operating losses
Statutory Federal income tax rate (as a percent)	21.00%	21.00%	35.00%
Alternative minimum tax credit which does not expire	$ 4.4	$ 8.8
Tax credit recovery period	2 years
Federal
Net operating losses
Operating loss carryforward	$ 1,581.1	1,504.9
Estimated effective tax rate on net operating losses	21.00%
State
Net operating losses
Operating loss carryforward	$ 766.4	$ 562.0
Estimated effective tax rate on net operating losses	3.36%