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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2021
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Reconciliation of the Carrying Amount of AROs

A reconciliation of the beginning and ending aggregate carrying amount of AROs is as follows:

 

(millions)

 

2021

 

 

2020

 

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.