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Asset Retirement Obligations (Schedule of Reconciliation of the Carrying Amount of AROs) (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Asset Retirement Obligation Disclosure [Abstract]    
Beginning balance $ 597 $ 489
Liabilities settled   (4)
Accretion expense 25 23
Revisions in estimated cash flows [1] (23) 89
Ending balance $ 599 $ 597
[1] The decrease in 2021 is due to the remeasurement of gas pipeline AROs. The increase in 2020 reflects revisions from the nuclear decommissioning cost study.