Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2019

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)	2019			2018
Beginning balance	$	541		$	529
Liabilities settled		(29	)		(15	)
Accretion expense		23			23
Revisions in estimated cash flows(1)		(46	)		4
Ending balance	$	489		$	541

(1)   The decrease in 2019 reflects a change in the estimated timing of cash flows for interim pipeline replacements and DOE recoveries.