Variable Interest Entities - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Variable Interest Entity [Line Items]
VIE, cash and cash equivalents	$ 882	$ 825	$ 4,108	$ 837
VIE. proved natural gas and oil properties	66,451	63,843
VIE. accumulated depreciation, depletion and amortization	62,726	59,365
VIE, other current liabilities	1,798	2,219
Proceeds from divestitures of proved and unproved properties	1,406	189	5,813
Net gain (loss) on sales of investments	(10)	0	$ 67
Mineral Acquisition Company I, L.P. [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets and Liabilities, Net		10
Proceeds from divestitures of proved and unproved properties	9
Net gain (loss) on sales of investments	(10)
Variable Interest Entities, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
VIE, cash and cash equivalents	1	1
VIE. proved natural gas and oil properties	488	488
VIE. accumulated depreciation, depletion and amortization	458	428
VIE, other current liabilities	$ 3	$ 8