Derivative Instruments and Hedging Activities - Fair Value Amounts and (Gain) Loss on Commodity Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Derivatives, Fair Value
Asset Derivative Instruments	$ 61			$ 61		$ 15
Liability Derivative Instruments	166			166		37
Total Cash Received in Settlement of Commodity Derivative Instruments	(106)		$ (1)	(314)	$ (15)
Total Non-cash Portion of Loss (Gain) on Commodity Derivative Instruments	264		(59)	83	167
Total Loss (Gain) on Commodity Derivative Instruments	158		(60)	(231)	152
Proceeds from derivative settlement		$ 160
Other Current Assets
Derivatives, Fair Value
Asset Derivative Instruments	61			61		14
Other Current Liabilities
Derivatives, Fair Value
Liability Derivative Instruments	151			151		36
Other Noncurrent Assets
Derivatives, Fair Value
Asset Derivative Instruments	0			0		1
Other Noncurrent Liabilities
Derivatives, Fair Value
Liability Derivative Instruments	15			15		$ 1
Crude Oil
Derivatives, Fair Value
Total Cash Received in Settlement of Commodity Derivative Instruments	(103)		7	(313)	(2)
Total Non-cash Portion of Loss (Gain) on Commodity Derivative Instruments	226		(54)	39	169
Total Loss (Gain) on Commodity Derivative Instruments	123		(47)	(274)	167
NGL
Derivatives, Fair Value
Total Cash Received in Settlement of Commodity Derivative Instruments	(3)		0	(3)	0
Total Non-cash Portion of Loss (Gain) on Commodity Derivative Instruments	10		0	0	0
Total Loss (Gain) on Commodity Derivative Instruments	7		0	(3)	0
Natural Gas
Derivatives, Fair Value
Total Cash Received in Settlement of Commodity Derivative Instruments	0		(8)	2	(13)
Total Non-cash Portion of Loss (Gain) on Commodity Derivative Instruments	28		(5)	44	(2)
Total Loss (Gain) on Commodity Derivative Instruments	$ 28		$ (13)	$ 46	$ (15)