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	3 Months Ended
	Mar. 31, 2019 USD ($) $ / bbl $ / MMBTU MBbls Bcf
Sold Fixed Price Swaps - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	195
Average price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.90
Fair Value	$ 23
Sold Fixed Price Swaps - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	921
Average price (in dollars per MMBtu, Bbl) | $ / bbl	62.13
Fair Value	$ 1
Sold Fixed Price Swaps - 2019 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,028
Average price (in dollars per MMBtu, Bbl) | $ / bbl	31.25
Fair Value	$ 7
Sold Fixed Price Swaps - 2019 | Ethane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	2,778
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	44
Fair Value	$ 3
Two-way Costless-collars - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	248
Fair Value	$ 1
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	72.30
Three-way Costless-collars - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	101
Fair Value	$ 13
Three-way Costless-collars - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	412
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	340
Fair Value	$ 39
Financial protection on production - 2019 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	1,581
Fair Value	$ 2
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	$ 3
Sold Fixed Price Swaps - 2020 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	366
Average price (in dollars per MMBtu, Bbl) | $ / bbl	65.68
Fair Value	$ 3
Sold Fixed Price Swaps - 2020 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	824
Average price (in dollars per MMBtu, Bbl) | $ / bbl	27.35
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	$ 2
Two-way Costless-collars - 2020 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	366
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	122
Fair Value	$ (2)
Three-way Costless-collars - 2020 Sold Calls | Natural Gas
Derivative [Line Items]
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.96
Financial protection on production - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	146
Fair Value	$ 1
Financial protection on production - 2020 | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	732
Fair Value	$ 5
Financial protection on production - 2020 | Propane
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	1,190
Three-way Costless-collars - 2021 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	37
Fair Value	$ (2)
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	85
Basis differential per MMBtu | $ / MMBTU	(0.50)
Fair Value	$ (13)
Sold Basis Swaps - 2020 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	59
Basis differential per MMBtu | $ / MMBTU	(0.44)
Fair Value	$ (8)
Sold Basis Swaps | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	144
Fair Value	$ (21)
Purchased fixed price swaps | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	206
Average price (in dollars per MMBtu, Bbl) | $ / bbl	69.10
Fair Value	$ (2)
Sold fixed price swaps | Oil
Derivative [Line Items]
Volume (Bcf, MBbls) | MBbls	1,127
Average price (in dollars per MMBtu, Bbl) | $ / bbl	63.41
Fair Value	$ 3
Purchased Call Options 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	30
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	$ 3
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	$ 3
Purchased call options | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	155
Fair Value	$ 6
Sold Call Options - 2019 | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	39
Cap price (in dollars per MMBtu, Bbl) | $ / MMBTU	3.50
Fair Value	$ (1)
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	$ (10)
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	$ (9)
Sold call options | Natural Gas
Derivative [Line Items]
Volume (Bcf, MBbls) | Bcf	290
Fair Value	$ (20)
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	$ 0
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]
Fair Value	$ 0
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	2.46
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	2.35
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	65.00
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	2.68
Purchased Puts | Three-Way Costless Collars - 2021 Purchased Puts | Natural Gas
Derivative [Line Items]
Floor price (in dollars per MMBtu, Bbl) | $ / MMBTU	2.60