XML 28 R17.htm IDEA: XBRL DOCUMENT

Asset Retirement Obligations

9 Months Ended

Sep. 30, 2020

Asset Retirement Obligation Disclosure [Abstract]

9. ASSET RETIREMENT OBLIGATIONS

A liability for the present value of an ARO is recognized when incurred if the liability can be reasonably estimated. Uncertainty about the timing or method of settlement of a conditional ARO is factored into the measurement of the liability when sufficient information exists, but such uncertainty is not a basis upon which to avoid liability recognition.

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

(millions)	Amount
AROs at December 31, 2019	$	489
Liabilities settled		(4	)
Accretion expense		17
Revisions in estimated cash flows ⁽¹⁾		89
AROs at September 30, 2020	$	591

(1)	The increase in 2020 reflects revisions from the nuclear decommissioning cost study.