Note 12 - Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Asset Retirement Obligation Activity

The following table provides asset retirement obligation activity (in millions):

	For the Year Ended December 31,
	2019			2018
Asset Retirement Obligations at start of period	$	48		$	43
Liabilities incurred in the current period		3			3
Liabilities settled in the current period		(6	)		(3	)
Accretion expense		2			2
Revision in estimated cash flows		1			3
Asset Retirement Obligations at end of period	$	48		$	48