Income Taxes - Net Deferred Income Tax Asset (Liability) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred income tax asset (liability):
Depreciation and amortization	$ (457.8)	$ (765.2)	$ (1,550.6)
Inventory basis differences	21.3	27.4	22.8
Accrued liabilities	87.9	68.5	50.8
Allowance for doubtful accounts	1.5	1.7	1.3
Research and development	58.9	61.7	63.7
Loss and credit carryforwards	292.5	292.4	244.2
Share-based compensation	16.2	18.1	20.6
Foreign tax credit	0.0	10.6	10.6
Federal benefit of unrecognized tax positions	17.0	24.3	22.8
Interest carryforwards	30.5	435.3	334.6
Other, net	28.2	3.0	14.7
Subtotal	96.2	177.8	(764.5)
Valuation allowance	(407.7)	(495.6)	(536.8)
Net deferred income tax asset (liability):	(311.5)	(317.8)	(1,301.3)
Non-current deferred income taxes	10.4	72.1	71.4
Non-current deferred income taxes	$ 321.9	$ 389.9	$ 1,372.7