Capitalized Exploratory Well Costs (Tables)

12 Months Ended

Dec. 31, 2019

Capitalized Exploratory Well Costs [Abstract]

Capitalized Exploratory Well Costs, Roll Forward [Table Text Block]

Net changes in capitalized exploratory well costs are presented in the table below.

	Capitalized Exploratory Well Costs
	2019		2018		2017
	(in millions)
Balance at January 1,	$	—	$	—	$	14.2
Additions to capitalized exploratory well costs	—		—		10.7
Reclassifications to proved properties	—		—		(3.6		)
Capitalized exploratory well costs charged to expense	—		—		(21.3		)
Balance at December 31,	$	—	$	—	$	—