Fair Value Measurements (Details) - Recurring [Member] - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
ASSETS:
Cash equivalents	$ 71.2	$ 23.3
Trust assets	0.2	0.2
Surety bonds		1.8
Derivative instruments	18.0	19.7
TOTAL	89.4	45.0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Contingent obligation – net	0.0	0.0
Derivative instruments	5.7	4.2
TOTAL	5.7	4.2
Level 1 [Member]
ASSETS:
Cash equivalents	71.2	23.3
Trust assets	0.2	0.2
Surety bonds		1.8
Derivative instruments	0.0	0.0
TOTAL	71.4	25.3
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Contingent obligation – net	0.0	0.0
Derivative instruments	0.0	0.0
TOTAL	0.0	0.0
Level 2 [Member]
ASSETS:
Cash equivalents	0.0	0.0
Trust assets	0.0	0.0
Surety bonds		0.0
Derivative instruments	11.4	9.1
TOTAL	11.4	9.1
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Contingent obligation – net	0.0	0.0
Derivative instruments	4.9	1.3
TOTAL	4.9	1.3
Level 3 [Member]
ASSETS:
Cash equivalents	0.0	0.0
Trust assets	0.0	0.0
Surety bonds		0.0
Derivative instruments	6.6	10.6
TOTAL	6.6	10.6
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Contingent obligation – net	0.0	0.0
Derivative instruments	0.8	2.9
TOTAL	$ 0.8	$ 2.9