Commitments and Contingencies (Details) - USD ($) $ in Millions			1 Months Ended		3 Months Ended
	Oct. 18, 2022	Dec. 13, 2019	Mar. 31, 2016	Jun. 30, 2015	Mar. 31, 2024	Dec. 31, 2019
Alaskan Way Viaduct Matter
Contingencies and Commitments
Value of claim filed			$ 57.2	$ 532.0
Settlement on judgment, awarded to other party		$ 57.2
Pre-tax charge, impact from jury verdict						$ 166.8
Pre-tax accrual, impact from jury verdict						25.7
Settlement on judgment						$ 57.2
Loss contingency, damages paid, value	$ 34.6
Alaskan Way Viaduct Matter | Seattle Tunnel Partners
Contingencies and Commitments
Ownership percentage in joint venture					45.00%
Seattle Tunnel Partners
Contingencies and Commitments
Value of counterclaim filed in excess of					$ 640.0