Employees - Financial Information Related to Pension Plans (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of the period (July 1, 2017 business combination)	$ 145.2	$ 146.9
Service cost	1.2	0.4	$ 1.2
Interest cost	2.7	5.2	2.7
Actuarial (gain) loss	6.5	(9.9)
Benefits paid	(2.4)	(9.1)
Other (effect of curtailment/settlement)	(6.3)	(2.5)
Projected benefit obligations at end of year	146.9	131.0	146.9
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of the period (July 1, 2017 business combination)	96.1	108.8
Actual (loss) gain on plan assets	9.8	(8.2)
Employer contribution	5.3	24.2
Benefits paid	(2.4)	(9.1)
Fair value of plan assets at end of year	108.8	115.7	108.8
Under-funded status at end of year	$ (38.1)	$ (15.3)	$ (38.1)