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ASSET RETIREMENT OBLIGATIONS
9 Months Ended
Sep. 30, 2021
Asset Retirement Obligation Disclosure [Abstract]  
ASSET RETIREMENT OBLIGATIONS ASSET RETIREMENT OBLIGATIONS
We have recorded AROs primarily for asbestos abatement at certain generation facilities, office buildings, and service centers; the dismantling of wind generation projects; the dismantling of solar generation projects; the disposal of polychlorinated biphenyls-contaminated transformers; and the closure of coal combustion residual landfills at certain generation facilities.

On our balance sheets, AROs are recorded within other long-term liabilities. The following table shows changes to our AROs during the nine months ended September 30, 2021:
(in millions)Nine Months Ended September 30, 2021
Balance as of January 1, 2021$45.5 
Accretion1.3 
Revisions to estimated cash flows (8.9)
(1)
Balance as of September 30, 2021$37.9 

(1)    This decrease was primarily due to revisions made to estimated cash flows for the legal requirement to dismantle, at retirement, our wind generation projects.