Other Property and Equipment Other Property and Equipment Gains (Losses) on Sales of Fixed Assets Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Net (gains) losses on sales of fixed assets	$ 3	$ 12	$ (4)
Buildings and Land [Member]
Property, Plant and Equipment [Line Items]
Net (gains) losses on sales of fixed assets	4	1	(3)
Natural Gas Compressors [Member]
Property, Plant and Equipment [Line Items]
Net (gains) losses on sales of fixed assets	(1)	10	0
Gas Gathering and Processing Equipment [Member]
Property, Plant and Equipment [Line Items]
Net (gains) losses on sales of fixed assets	0	0	(1)
Exploration and Production Equipment [Member]
Property, Plant and Equipment [Line Items]
Net (gains) losses on sales of fixed assets	0	1	0
Other Assets [Member]
Property, Plant and Equipment [Line Items]
Net (gains) losses on sales of fixed assets	$ 3	$ 12	$ (4)