Financial Statements for Guarantors of the Senior Notes - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets:
Cash and cash equivalents	$ 97.6			$ 179.2
Receivables, net of allowance	304.7			276.6
Income tax receivable	21.1			40.4
Inventory	632.9			524.7
Property, plant, and equipment, net	6,916.7			6,334.4
Investments in and advances to subsidiaries	0.0			0.0
Restricted cash	117.5			171.6
Goodwill and other assets	552.6			462.3
Total assets	8,643.1			7,989.2
Liabilities:
Accounts payable	250.8			212.1
Accrued liabilities	368.9			368.3
Debt	4,685.2			4,029.2
Deferred income	0.0			17.7
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	784.1			743.1
Advances from subsidiaries	0.0			0.0
Other liabilities	94.8			56.8
Total stockholders' equity	2,459.3	$ 2,529.6	$ 2,565.1	2,562.0	$ 4,643.4	$ 4,671.8	$ 4,834.6	$ 4,858.0
Total liabilities and stockholders' equity	8,643.1			7,989.2
Reportable legal entities | Parent
Assets:
Cash and cash equivalents	87.4			154.7
Receivables, net of allowance	2.9			12.5
Income tax receivable	21.1			40.4
Inventory	0.0			0.0
Property, plant, and equipment, net	42.3			42.0
Investments in and advances to subsidiaries	4,655.8			4,558.6
Restricted cash	0.0			0.0
Goodwill and other assets	252.1			205.1
Total assets	5,061.6			5,013.3
Liabilities:
Accounts payable	4.3			8.6
Accrued liabilities	179.8			184.3
Debt	472.7			397.4
Deferred income				0.0
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	0.0			0.0
Advances from subsidiaries	1,893.8			1,804.2
Other liabilities	51.7			56.8
Total stockholders' equity	2,459.3			2,562.0
Total liabilities and stockholders' equity	5,061.6			5,013.3
Reportable legal entities | Combined Guarantor Subsidiaries
Assets:
Cash and cash equivalents	2.3			4.1
Receivables, net of allowance	227.6			181.8
Income tax receivable	0.0			0.0
Inventory	592.4			485.8
Property, plant, and equipment, net	1,275.9			1,436.3
Investments in and advances to subsidiaries	3,167.3			2,981.7
Restricted cash	0.0			0.0
Goodwill and other assets	300.0			197.9
Total assets	5,565.5			5,287.6
Liabilities:
Accounts payable	171.5			134.0
Accrued liabilities	34.4			55.4
Debt	0.0			0.0
Deferred income				16.5
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	860.4			790.3
Advances from subsidiaries	0.0			0.0
Other liabilities	41.9			0.0
Total stockholders' equity	4,457.3			4,291.4
Total liabilities and stockholders' equity	5,565.5			5,287.6
Reportable legal entities | Combined Non-Guarantor Subsidiaries
Assets:
Cash and cash equivalents	32.7			59.1
Receivables, net of allowance	74.2			82.3
Income tax receivable	0.0			0.0
Inventory	40.6			40.9
Property, plant, and equipment, net	6,387.5			5,579.7
Investments in and advances to subsidiaries	357.0			661.1
Restricted cash	92.7			132.9
Goodwill and other assets	62.8			106.8
Total assets	7,047.5			6,662.8
Liabilities:
Accounts payable	74.7			69.9
Accrued liabilities	158.6			128.7
Debt	4,212.5			3,631.8
Deferred income				1.2
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	2.2			0.0
Advances from subsidiaries	0.0			0.0
Other liabilities	1.2			0.0
Total stockholders' equity	2,598.3			2,831.2
Total liabilities and stockholders' equity	7,047.5			6,662.8
Eliminations
Assets:
Cash and cash equivalents	(24.8)			(38.7)
Receivables, net of allowance	0.0			0.0
Income tax receivable	0.0			0.0
Inventory	(0.1)			(2.0)
Property, plant, and equipment, net	(789.0)			(723.6)
Investments in and advances to subsidiaries	(8,180.1)			(8,201.4)
Restricted cash	24.8			38.7
Goodwill and other assets	(62.3)			(47.5)
Total assets	(9,031.5)			(8,974.5)
Liabilities:
Accounts payable	0.3			(0.4)
Accrued liabilities	(3.9)			(0.1)
Debt	0.0			0.0
Deferred income				0.0
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	(78.5)			(47.2)
Advances from subsidiaries	(1,893.8)			(1,804.2)
Other liabilities	0.0			0.0
Total stockholders' equity	(7,055.6)			(7,122.6)
Total liabilities and stockholders' equity	$ (9,031.5)			$ (8,974.5)