Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2017

Asset Retirement Obligation Disclosure [Abstract]

Schedule of Asset Retirement Obligations [Table Text Block]

AROs consist of the following (in millions):

	As of December 31,
	2017		2016
Trojan decommissioning activities	$	45	$	44
Utility plant	109		105
Non-utility property	13		12
Asset retirement obligations	$	167	$	161

Schedule of Change in Asset Retirement Obligation [Table Text Block]

The following is a summary of the changes in the Company’s AROs (in millions):

	Years Ended December 31,
	2017			2016			2015
Balance as of beginning of year	$	161		$	151		$	116
Liabilities incurred	2			1			2
Liabilities settled	(3		)	(3		)	(4		)
Accretion expense	7			7			7
Revisions in estimated cash flows	—			5			30
Balance as of end of year	$	167		$	161		$	151