Employees - Financial Information Related to Pension Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in projected benefit obligation:
Benefit obligation at beginning of year	$ 105.3	$ 140.8
Interest cost	5.3	3.7	$ 3.5
Actuarial loss (gain)	2.0	(33.5)
Benefits paid	(5.9)	(5.7)
Projected benefit obligations at end of year	106.7	105.3	140.8
Change in plan assets:
Fair value of plan assets at beginning of year	102.2	137.9
Actual gain (loss) on plan assets	7.9	(30.0)
Benefits paid	(5.9)	(5.7)
Fair value of plan assets at end of year	104.2	102.2	$ 137.9
Under-funded status at end of year	$ (2.5)	$ (3.1)