Financial Statements for Guarantors of the Senior Notes - Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets:
Cash and cash equivalents	$ 102.8		$ 179.2
Receivables, net of allowance	351.7		276.6
Income tax receivable	21.0		40.4
Inventory	600.5		524.7
Property, plant, and equipment, net	6,869.6		6,334.4
Investments in and advances to subsidiaries	0.0		0.0
Restricted cash	113.7		171.6
Goodwill and other assets	516.6		462.3
Total assets	8,575.9		7,989.2
Liabilities:
Accounts payable	217.7		212.1
Accrued liabilities	346.3		368.3
Debt	4,615.9		4,029.2
Deferred income	0.0		17.7
Deferred income taxes	769.0		743.1
Advances from subsidiaries	0.0		0.0
Other liabilities	97.4		56.8
Total stockholders' equity	2,529.6	$ 2,565.1	2,562.0	$ 4,671.8	$ 4,834.6	$ 4,858.0
Total liabilities and stockholders' equity	8,575.9		7,989.2
Reportable legal entities | Parent
Assets:
Cash and cash equivalents	93.3		154.7
Receivables, net of allowance	3.5		12.5
Income tax receivable	21.0		40.4
Inventory	0.0		0.0
Property, plant, and equipment, net	43.1		42.0
Investments in and advances to subsidiaries	4,661.5		4,558.6
Restricted cash	0.0		0.0
Goodwill and other assets	229.4		205.1
Total assets	5,051.8		5,013.3
Liabilities:
Accounts payable	9.4		8.6
Accrued liabilities	156.9		184.3
Debt	397.6		397.4
Deferred income			0.0
Deferred income taxes	0.0		0.0
Advances from subsidiaries	1,904.7		1,804.2
Other liabilities	53.6		56.8
Total stockholders' equity	2,529.6		2,562.0
Total liabilities and stockholders' equity	5,051.8		5,013.3
Reportable legal entities | Combined Guarantor Subsidiaries
Assets:
Cash and cash equivalents	0.0		4.1
Receivables, net of allowance	253.2		181.8
Income tax receivable	0.0		0.0
Inventory	554.5		485.8
Property, plant, and equipment, net	1,284.3		1,436.3
Investments in and advances to subsidiaries	3,075.1		2,981.7
Restricted cash	0.0		0.0
Goodwill and other assets	275.5		197.9
Total assets	5,442.6		5,287.6
Liabilities:
Accounts payable	137.2		134.0
Accrued liabilities	53.3		55.4
Debt	0.0		0.0
Deferred income			16.5
Deferred income taxes	831.3		790.3
Advances from subsidiaries	0.0		0.0
Other liabilities	42.6		0.0
Total stockholders' equity	4,378.2		4,291.4
Total liabilities and stockholders' equity	5,442.6		5,287.6
Reportable legal entities | Combined Non-Guarantor Subsidiaries
Assets:
Cash and cash equivalents	34.9		59.1
Receivables, net of allowance	95.0		82.3
Income tax receivable	0.0		0.0
Inventory	46.1		40.9
Property, plant, and equipment, net	6,344.7		5,579.7
Investments in and advances to subsidiaries	426.3		661.1
Restricted cash	88.3		132.9
Goodwill and other assets	67.3		106.8
Total assets	7,102.6		6,662.8
Liabilities:
Accounts payable	71.7		69.9
Accrued liabilities	140.3		128.7
Debt	4,218.3		3,631.8
Deferred income			1.2
Deferred income taxes	1.4		0.0
Advances from subsidiaries	0.0		0.0
Other liabilities	1.2		0.0
Total stockholders' equity	2,669.7		2,831.2
Total liabilities and stockholders' equity	7,102.6		6,662.8
Eliminations
Assets:
Cash and cash equivalents	(25.4)		(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	(802.5)		(723.6)
Investments in and advances to subsidiaries	(8,162.9)		(8,201.4)
Restricted cash	25.4		38.7
Goodwill and other assets	(55.6)		(47.5)
Total assets	(9,021.1)		(8,974.5)
Liabilities:
Accounts payable	(0.6)		(0.4)
Accrued liabilities	(4.2)		(0.1)
Debt	0.0		0.0
Deferred income			0.0
Deferred income taxes	(63.7)		(47.2)
Advances from subsidiaries	(1,904.7)		(1,804.2)
Other liabilities	0.0		0.0
Total stockholders' equity	(7,047.9)		(7,122.6)
Total liabilities and stockholders' equity	$ (9,021.1)		$ (8,974.5)