Guarantee of Securities of Subsidiaries Guarantee of Securities of Subsidiaries Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ 108.1	$ 97.2
Other comprehensive income (loss):
Reclassification adjustment transferred to Net income from cash flow hedges	0.3	0.6
Pension and other postretirement benefit costs, net of tax	0.5	0.3
Total Comprehensive Income (Loss)	108.9	98.1
Reportable Legal Entities | Parent Guarantor
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	108.1	97.2
Other comprehensive income (loss):
Reclassification adjustment transferred to Net income from cash flow hedges	0.3	0.6
Pension and other postretirement benefit costs, net of tax	0.5	0.3
Total Comprehensive Income (Loss)	108.9	98.1
Reportable Legal Entities | Subsidiary Issuer
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	89.2	82.9
Other comprehensive income (loss):
Reclassification adjustment transferred to Net income from cash flow hedges	0.3	0.6
Pension and other postretirement benefit costs, net of tax	0.5	0.3
Total Comprehensive Income (Loss)	90.0	83.8
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	137.8	125.6
Other comprehensive income (loss):
Reclassification adjustment transferred to Net income from cash flow hedges	0.3	0.2
Pension and other postretirement benefit costs, net of tax	0.5	0.3
Total Comprehensive Income (Loss)	138.6	126.1
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	(227.0)	(208.5)
Other comprehensive income (loss):
Reclassification adjustment transferred to Net income from cash flow hedges	(0.6)	(0.8)
Pension and other postretirement benefit costs, net of tax	(1.0)	(0.6)
Total Comprehensive Income (Loss)	$ (228.6)	$ (209.9)