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Asset Retirement Obligations (Tables)
6 Months Ended
Mar. 31, 2021
Asset Retirement Obligation Disclosure [Abstract]  
Asset Retirement Obligation Activity
Asset Retirement Obligation Activity
 NuclearNon-NuclearTotal
Balance at September 30, 2020$3,278 $3,507 $6,785 (1)
Settlements(3)(77)(80)
Revisions in estimate 106 108 
Accretion (recorded as regulatory asset)74 31 105 
Balance at March 31, 2021$3,351 $3,567 $6,918 (1)
Note
(1) Includes $271 million and $345 million at March 31, 2021, and September 30, 2020, respectively, in Current liabilities.

The revisions in non-nuclear estimates increased $106 million for the six months ended March 31, 2021. These increases were primarily driven by revisions of certain CCR closure liabilities at Shawnee, Paradise, and Colbert, resulting from revised engineering estimates for construction costs, new vendor bids, modified closure designs, and expected costs associated with post-closure care of the closed areas.