Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2024

Asset Retirement Obligation Disclosure [Abstract]

Schedule of changes to asset retirement obligations

The following table shows changes to our AROs during the years ended December 31:

(in millions)	2024			2023			2022
Balance as of January 1	$	374.2		$	479.3		$	462.0
Accretion	18.8			17.2			16.1
Additions	192.7		(1)	24.0			12.8
Revisions to estimated cash flows	6.4			(133.5)		(2)	2.2
Liabilities settled	(12.1)			(12.8)			(13.8)
Balance as of December 31	$	580.0		$	374.2		$	479.3

(1)    AROs increased primarily as a result of AROs being recorded related to the new EPA CCR Rule that was enacted in April 2024. See Note 24, Commitments and Contingencies, for more information.

(2)    AROs decreased primarily due to revisions made to estimated cash flows for changes in removal cost estimates and settlements dates for mains and services at PGL and NSG.