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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2020
Asset Retirement Obligation [Abstract]  
Changes In Liability For Asset Retirement Obligations
Changes in our liability for asset retirement obligations for the years 2020 and 2019 are presented in the table below:
(in millions)20202019
Beginning Balance$416.9 $352.0 
Accretion recorded as a regulatory asset/liability17.3 15.7 
Additions5.5 — 
Settlements(13.9)(5.4)
Change in estimated cash flows
86.0 
(1)
54.6 
(2)
Other(16.2)
(3)
— 
Ending Balance$495.6 $416.9 
(1)The change in estimated cash flows for 2020 is primarily attributed to revisions to the estimated costs associated with refining the CCR compliance plan, changes in estimated costs for electric generating stations and the changes in estimated costs for retirement of gas mains. See Note 20-D. "Environmental Matters" for additional information on CCRs.
(2)The change in estimated cash flows for 2019 is primarily attributed to changes in estimated costs and settlement timing for electric generating stations and the changes in estimated costs for retirement of gas mains.
(3)Represents the Columbia of Massachusetts Asset Retirement Obligations that were included in the sale of the Massachusetts Business that occurred on October 9, 2020.