Derivatives and Risk Management (Schedule of Derivative Instruments Notional Amount, Weighted Average Contract Prices and Fair Value) (Details) - Not Designated as Hedging Instrument MBbls in Thousands, $ in Millions, Bcf in Billions	9 Months Ended
	Sep. 30, 2019 USD ($) $ / bbl $ / MMBTU MBbls Bcf
Sold Fixed Price Swaps - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	61
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.89
Fair Value	$ 28
Sold Fixed Price Swaps - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	632
Average price (in dollars per MMBtu, Bbl) | $ / bbl	60.65
Fair Value	$ 4
Sold Fixed Price Swaps - 2019 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	978
Average price (in dollars per MMBtu, Bbl) | $ / bbl	30.18
Fair Value	$ 11
Sold Fixed Price Swaps - 2019 | Ethane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,194
Average price (in dollars per MMBtu, Bbl) | $ / bbl	10.53
Fair Value	$ 6
Two-way Costless-collars - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	6
Fair Value	$ 2
Two-way Costless-collars - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	382
Fair Value	$ 3
Two-way Costless-collars - 2019 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	138
Fair Value	$ 1
Two-way Costless-collars - 2019 Purchased Puts | Propane
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	25.62
Two-way Costless-collars - 2019 Sold Calls | Natural Gas
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.92
Two-way Costless-collars - 2019 Sold Calls | Oil
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / bbl	67.16
Two-way Costless-collars - 2019 Sold Calls | Propane
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / bbl	28.77
Three-way Costless-collars - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	44
Fair Value	$ 13
Three-way Costless-collars - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	138
Three-way Costless-collars - 2019 Sold Calls | Natural Gas
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.15
Three-way Costless-collars - 2019 Sold Calls | Oil
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / bbl	63.67
Financial protection on production - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	111
Fair Value	$ 43
Financial protection on production - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	1,152
Fair Value	$ 7
Financial protection on production - 2019 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	1,116
Fair Value	$ 12
Sold Fixed Price Swaps - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	151
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.58
Fair Value	$ 45
Sold Fixed Price Swaps - 2020 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	1,556
Average price (in dollars per MMBtu, Bbl) | $ / bbl	60.18
Fair Value	$ 14
Sold Fixed Price Swaps - 2020 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,928
Average price (in dollars per MMBtu, Bbl) | $ / bbl	25.58
Fair Value	$ 18
Sold Fixed Price Swaps - 2020 | Ethane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	3,843
Average price (in dollars per MMBtu, Bbl) | $ / bbl	9.80
Fair Value	$ 7
Two-way Costless-collars - 2020 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	366
Fair Value	$ 4
Two-way Costless-collars - 2020 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	366
Fair Value	$ 2
Two-way Costless-collars - 2020 Sold Calls | Oil
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / bbl	69.80
Two-way Costless-collars - 2020 Sold Calls | Propane
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / bbl	29.40
Three-Way Costless Collars - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	209
Fair Value	$ 22
Three-Way Costless Collars - 2020 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	915
Fair Value	$ 3
Three-way Costless-collars - 2020 Sold Calls | Natural Gas
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.98
Three-way Costless-collars - 2020 Sold Calls | Oil
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / bbl	61.75
Financial protection on production - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	360
Fair Value	$ 67
Financial protection on production - 2020 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,837
Fair Value	$ 21
Financial protection on production - 2020 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	3,294
Fair Value	$ 20
Three-way Costless-collars - 2021 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	134
Fair Value	$ (1)
Three-way Costless-collars - 2021 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	730
Fair Value	$ 1
Three-Way Costless Collars - 2021 Sold Calls | Natural Gas
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.85
Three-Way Costless Collars - 2021 Sold Calls | Oil
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / bbl	59.50
Sold Fixed Price Swaps - 2021 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	456
Average price (in dollars per MMBtu, Bbl) | $ / bbl	22.24
Fair Value	$ 1
Three-Way Costless Collars-2022 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	23
Fair Value	$ 0
Three-way Costless Collars 2022 - Sold Calls | Natural Gas
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.14
Sold Basis Swaps - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	35
Basis differential per MMBtu | $ / MMBTU	(0.40)
Fair Value	$ 9
Sold Basis Swaps - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	141
Basis differential per MMBtu | $ / MMBTU	(0.31)
Fair Value	$ (13)
Sold Basis Swaps - 2021 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	65
Basis differential per MMBtu | $ / MMBTU	(0.48)
Fair Value	$ (1)
Sold Basis Swaps 2022 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	45
Basis differential per MMBtu | $ / MMBTU	(0.50)
Fair Value	$ 0
Sold Basis Swaps | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	286
Fair Value	$ (5)
Purchased fixed price swaps | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	69
Average price (in dollars per MMBtu, Bbl) | $ / bbl	69.10
Fair Value	$ (1)
Sold fixed price swaps | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	701
Average price (in dollars per MMBtu, Bbl) | $ / bbl	61.48
Fair Value	$ 5
Purchased Call Options 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	5
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.50
Fair Value	$ 0
Purchased Call Options - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	68
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.63
Fair Value	$ 1
Purchased Call Options - 2021 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	57
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.52
Fair Value	$ 2
Purchased call options | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	130
Fair Value	$ 3
Sold Call Options - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	13
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.50
Fair Value	$ 0
Sold Call Options - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	137
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.39
Fair Value	$ (5)
Sold Call Options - 2021 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	114
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.33
Fair Value	$ (6)
Sold Call Options - 2023 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	6
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.00
Fair Value	$ (1)
Sold Call Options - 2024 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	9
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.00
Fair Value	$ (2)
Sold call options | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	279
Fair Value	$ (14)
Purchased Fixed Price Swaps, Storage, 2019
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	0
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.90
Basis differential per MMBtu | $ / MMBTU	0
Fair Value	$ 0
Purchased Basis Swaps Storage, 2019
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	0
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	0
Basis differential per MMBtu | $ / MMBTU	(0.61)
Fair Value	$ 0
Storage 2019
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	0
Fair Value	$ 0
Purchased Fixed Price Swaps, Storage, 2020
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	0
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.37
Basis differential per MMBtu | $ / MMBTU	0
Fair Value	$ 0
Purchased Basis Swaps, Storage, 2020
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	0
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	0
Basis differential per MMBtu | $ / MMBTU	(0.32)
Fair Value	$ 0
Fixed Price Swap, Storage, 2020
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	2
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.06
Basis differential per MMBtu | $ / MMBTU	0
Fair Value	$ 1
Sold Basis Swaps, Storage, 2020
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	0
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	0
Basis differential per MMBtu | $ / MMBTU	(0.32)
Fair Value	$ 0
Storage 2020
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	2
Fair Value	$ 1
Short Puts | Three-way Costless-collars - 2019 Sold Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.43
Short Puts | Three-way Costless-collars - 2019 Sold Puts | Oil
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	45.00
Short Puts | Three-way Costless-collars - 2020 Sold Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.34
Short Puts | Three-way Costless-collars - 2020 Sold Puts | Oil
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	45.00
Short Puts | Three-Way Costless Collars - 2021 Sold Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.27
Short Puts | Three-Way Costless Collars - 2021 Sold Puts | Oil
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	45.00
Short Puts | Three-Way Costless Collars 2022 - Sold Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.30
Purchased Puts | Two-way Costless-collars - 2019 Purchased Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.78
Purchased Puts | Two-way Costless-collars - 2019 Purchased Puts | Oil
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	61.45
Purchased Puts | Three-way Costless-collars - 2019 Purchased Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.82
Purchased Puts | Three-way Costless-collars - 2019 Purchased Puts | Oil
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	55.00
Purchased Puts | Two-way Costless-collars - 2020 Purchased Puts | Oil
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	60.00
Purchased Puts | Two-way Costless-collars - 2020 Purchased Puts | Propane
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	25.20
Purchased Puts | Three-way Costless-collars - 2020 Purchased Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.67
Purchased Puts | Three-way Costless-collars - 2020 Purchased Puts | Oil
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	55.00
Purchased Puts | Three-Way Costless Collars - 2021 Purchased Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.55
Purchased Puts | Three-Way Costless Collars - 2021 Purchased Puts | Oil
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / bbl	53.00
Purchased Puts | Three Way Costless Collars 2022 - Purchased Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.70