Oil and Natural Gas Property Transactions - Narrative (Details) MMcf in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) well	Jun. 30, 2017 USD ($) well MMcf	Jun. 30, 2018 USD ($) a well	Jun. 30, 2017 USD ($) a well MMcf
Business Acquisition [Line Items]
Proceeds from divestitures of proved and unproved properties			$ 384	$ 951
Mid-Continent [Member]
Business Acquisition [Line Items]
Proceeds from divestitures of proved and unproved properties			$ 491
Number of net acres | a			238,500
Productive gas wells, number of wells, net | well	3,200		3,200
Other properties [Member]
Business Acquisition [Line Items]
Proceeds from divestitures of proved and unproved properties	$ 5	$ 63	$ 23	83
Haynesville Shale [Member]
Business Acquisition [Line Items]
Proceeds from divestitures of proved and unproved properties				$ 915
Number of net acres | a				119,500
Productive gas wells, number of wells, net | well		576		576
Haynesville Shale [Member] | Natural gas [Member]
Business Acquisition [Line Items]
Proved developed reserves (volume) | MMcf		80		80