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	6 Months Ended
	Jun. 30, 2019 USD ($) $ / bbl $ / MMBTU MBbls Bcf
Sold Fixed Price Swaps - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	131
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.92
Fair Value	$ 75
Sold Fixed Price Swaps - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	1,003
Average price (in dollars per MMBtu, Bbl) | $ / bbl	60.89
Fair Value	$ 4
Sold Fixed Price Swaps - 2019 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	1,955
Average price (in dollars per MMBtu, Bbl) | $ / bbl	30.18
Fair Value	$ 14
Sold Fixed Price Swaps - 2019 | Ethane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	1,858
Average price (in dollars per MMBtu, Bbl) | $ / bbl	13.90
Fair Value	$ 10
Two-way Costless-collars - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	25
Fair Value	$ 13
Two-way Costless-collars - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	764
Fair Value	$ 4
Two-way Costless-collars - 2019 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	276
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	67
Fair Value	$ 22
Three-way Costless-collars - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	276
Three-way Costless-collars - 2019 Sold Calls | Natural Gas
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.22
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	223
Fair Value	$ 110
Financial protection on production - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,043
Fair Value	$ 8
Financial protection on production - 2019 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,231
Fair Value	$ 15
Sold Fixed Price Swaps - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	24
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.88
Fair Value	$ 8
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	$ 7
Sold Fixed Price Swaps - 2020 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,196
Average price (in dollars per MMBtu, Bbl) | $ / bbl	26.97
Fair Value	$ 6
Sold Fixed Price Swaps - 2020 | Ethane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	732
Average price (in dollars per MMBtu, Bbl) | $ / bbl	13.49
Fair Value	$ 2
Two-way Costless-collars - 2020 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	366
Fair Value	$ 3
Two-way Costless-collars - 2020 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	366
Fair Value	$ 1
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	148
Fair Value	$ 10
Three-Way Costless Collars - 2020 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	641
Fair Value	$ 1
Three-way Costless-collars - 2020 Sold Calls | Natural Gas
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.97
Three-way Costless-collars - 2020 Sold Calls | Oil
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / bbl	63.36
Financial protection on production - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	172
Fair Value	$ 18
Financial protection on production - 2020 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,563
Fair Value	$ 11
Financial protection on production - 2020 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,562
Fair Value	$ 7
Three-way Costless-collars - 2021 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	37
Fair Value	$ (1)
Three-Way Costless Collars - 2021 Sold Calls | Natural Gas
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.93
Sold Basis Swaps - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	80
Basis differential per MMBtu | $ / MMBTU	(0.45)
Fair Value	$ (6)
Sold Basis Swaps - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	132
Basis differential per MMBtu | $ / MMBTU	(0.34)
Fair Value	$ (10)
Sold Basis Swaps - 2021 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	28
Basis differential per MMBtu | $ / MMBTU	(0.51)
Fair Value	$ (1)
Sold Basis Swaps | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	240
Fair Value	$ (17)
Purchased fixed price swaps | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	138
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	1,141
Average price (in dollars per MMBtu, Bbl) | $ / bbl	61.88
Fair Value	$ 5
Purchased Call Options 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	17
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	$ 2
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	142
Fair Value	$ 4
Sold Call Options - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	26
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	$ (8)
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	$ (8)
Sold call options | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	277
Fair Value	$ (16)
Purchased Fixed Price Swaps, Storage, 2019
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	1
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.87
Basis differential per MMBtu | $ / MMBTU	0
Fair Value	$ (1,000)
Purchased Basis Swaps Storage, 2019
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	1
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	0
Basis differential per MMBtu | $ / MMBTU	(0.53)
Fair Value	$ 0
Storage 2019
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	2
Fair Value	$ (1,000)
Fixed Price Swap, Storage, 2020
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	1
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.14
Basis differential per MMBtu | $ / MMBTU	0
Fair Value	$ 0
Short Puts | Three-way Costless-collars - 2019 Sold Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.47
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	2.36
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	2.35
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	2.88
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	2.60