Pension Benefits - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) employees	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost		$ 27.5	$ 30.6	$ 28.9
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Number of participants and beneficiaries | employees		3,100
Contribution as a percentage of compensation		3.00%
Benefits paid	$ 90.0	$ 100.9	13.7
Settlement benefits		205.7
Settlement of asset retirement obligations		70.2
Settlement of asset retirement obligations		55.5
Assets for plan benefits		16.4
Unfunded liability		(16.3)	(23.6)
Pension expense		71.1	3.8	0.6
Unrecognized pension gain (loss) arising during the year		0.0	12.0	6.0
Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Unfunded liability		21.8	22.0
Pension expense		1.0	0.8	0.7
Unrecognized pension gain (loss) arising during the year		$ (0.7)	$ 4.8	$ 1.3