Derivatives and Risk Management (Summary of Before Tax Effect of Fair Value Hedges not Designated for Hedge Accounting) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	$ 246	$ (22)
Settled Gain (Loss) on Derivatives Recognized in Earnings	93	(10)
Total gain (loss) on derivatives	339	(32)
Purchased fixed price swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(5)	4
Settled Gain (Loss) on Derivatives Recognized in Earnings	0	(1)
Purchased fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	(1)	0
Fixed price swaps | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	118	(13)
Settled Gain (Loss) on Derivatives Recognized in Earnings	9	2
Fixed price swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	103	(2)
Settled Gain (Loss) on Derivatives Recognized in Earnings	5	(6)
Fixed price swaps | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	36	(4)
Settled Gain (Loss) on Derivatives Recognized in Earnings	10	2
Fixed price swaps | Ethane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	12	7
Settled Gain (Loss) on Derivatives Recognized in Earnings	6	1
Two-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	19	(7)
Settled Gain (Loss) on Derivatives Recognized in Earnings	3	1
Two-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(4)	(1)
Settled Gain (Loss) on Derivatives Recognized in Earnings	6	(1)
Two-way costless collars | Propane
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	2	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	0
Three-way costless collars | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	25	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	0
Three-way costless collars | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(51)	2
Settled Gain (Loss) on Derivatives Recognized in Earnings	36	(4)
Basis swaps | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	(10)
Settled Gain (Loss) on Derivatives Recognized in Earnings	16	(4)
Purchased call options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	1	0
Sold call options | Oil
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	1	0
Sold call options | Natural Gas
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(6)	2
Storage - fixed price swap | Natural Gas Storage
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	(1)	0
Settled Gain (Loss) on Derivatives Recognized in Earnings	1	0
Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Unsettled Gain (Loss) on Derivatives Recognized in Earnings	$ (1)	$ 0