Derivatives and Risk Management (Schedule of Derivative Instruments Notional Amount, Weighted Average Contract Prices and Fair Value) (Details) - Not Designated as Hedging Instrument [Member] $ in Millions, ft³ in Billions	6 Months Ended
	Jun. 30, 2018 USD ($) $ / bbl $ / MMBTU MBbls ft³
Sold Fixed Price Swaps -2018 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	156
Average price	2.96
Fair Value | $	$ 1
Sold Fixed Price Swaps -2018 [Member] | Propane [Member]
Derivative [Line Items]
Volume | MBbls	1,555
Average price | $ / bbl	34.86
Fair Value | $	$ (7)
Sold Fixed Price Swaps -2018 [Member] | Ethane [Member]
Derivative [Line Items]
Volume | MBbls	1,398
Average price | $ / bbl	11.85
Fair Value | $	$ (2)
Sold Fixed Price Swaps -2019 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	147
Average price	2.93
Fair Value | $	$ 25
Sold Fixed Price Swaps -2019 [Member] | Propane [Member]
Derivative [Line Items]
Volume | MBbls	1,324
Average price | $ / bbl	32.43
Fair Value | $	$ (2)
Sold Fixed Price Swaps -2019 [Member] | Ethane [Member]
Derivative [Line Items]
Volume | MBbls	1,734
Average price | $ / bbl	11.59
Sold Fixed Price Swaps -2020 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	2
Average price	2.77
Fair Value | $
Storage Purchased Fixed Price Swaps - 2018 [Member]
Derivative [Line Items]
Volume | ft³	1
Average price	2.76
Storage Sold Fixed Price Swaps - 2018 [Member]
Derivative [Line Items]
Average price	2.89
Storage Sold Fixed Price Swaps - 2019 [Member]
Derivative [Line Items]
Volume | ft³	1
Average price	3.03
Two-way Costless-collars - 2018 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	6
Fair Value | $
Two-way Costless-collars - 2018 Purchased Puts [Member] | Natural Gas [Member]
Derivative [Line Items]
Floor price per MMBtu	2.90
Two-way Costless-collars - 2018 Sold Calls [Member] | Natural Gas [Member]
Derivative [Line Items]
Cap price per MMBtu	3.27
Two-way Costless-collars - 2019 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	53
Fair Value | $	$ 6
Two-way Costless-collars - 2019 Purchased Puts [Member] | Natural Gas [Member]
Derivative [Line Items]
Floor price per MMBtu	2.80
Two-way Costless-collars - 2019 Sold Calls [Member] | Natural Gas [Member]
Derivative [Line Items]
Cap price per MMBtu	2.98
Three-way Costless-collars - 2018 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	143
Fair Value | $	$ 13
Three-way Costless-collars - 2018 Sold Puts [Member] | Natural Gas [Member]
Derivative [Line Items]
Floor price per MMBtu	2.40
Three-way Costless-collars - 2018 Purchased Puts [Member] | Natural Gas [Member]
Derivative [Line Items]
Floor price per MMBtu	2.97
Three-way Costless-collars - 2018 Sold Calls [Member] | Natural Gas [Member]
Derivative [Line Items]
Cap price per MMBtu	3.37
Three-Way Costless Collars - 2019 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	133
Fair Value | $	$ 12
Three-way Costless-collars - 2019 Sold Puts [Member] | Natural Gas [Member]
Derivative [Line Items]
Floor price per MMBtu	2.49
Three-way Costless-collars - 2019 Purchased Puts [Member] | Natural Gas [Member]
Derivative [Line Items]
Floor price per MMBtu	2.93
Three-way Costless-collars - 2019 Sold Calls [Member] | Natural Gas [Member]
Derivative [Line Items]
Cap price per MMBtu	3.34
Three-way Costless-collars - 2020 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	47
Fair Value | $	$ 1
Three-Way Costless Collars - 2020 Sold Puts [Member] | Natural Gas [Member]
Derivative [Line Items]
Floor price per MMBtu	2.43
Three-Way Costless Collars - 2020 Purchased Puts [Member] | Natural Gas [Member]
Derivative [Line Items]
Floor price per MMBtu	2.80
Three-Way Costless Collars - 2020 Sold Calls [Member] | Natural Gas [Member]
Derivative [Line Items]
Cap price per MMBtu	3.09
Financial protection on production - 2018 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	305
Fair Value | $	$ 14
Financial protection on production - 2019 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	333
Fair Value | $	$ 43
Financial protection on production - 2020 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	49
Fair Value | $	$ 1
Financial protection on storage - 2018 [Member]
Derivative [Line Items]
Volume | ft³	2
Financial protection on storage - 2019 [Member]
Derivative [Line Items]
Volume | ft³	2
Sold Basis Swaps - 2018 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	44
Basis differential per MMBtu	(0.58)
Fair Value | $	$ (2)
Sold Basis Swaps - 2019 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	11
Basis differential per MMBtu	1.24
Fair Value | $	$ (3)
Sold Basis Swaps [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	55
Fair Value | $	$ (5)
Storage Purchased Basis Swaps - 2018 [Member]
Derivative [Line Items]
Volume | ft³	1
Basis differential per MMBtu	(0.88)
Storage Sold Basis Swaps - 2018 [Member]
Derivative [Line Items]
Basis differential per MMBtu	(0.63)
Storage Sold Basis Swaps - 2019 [Member]
Derivative [Line Items]
Volume | ft³	1
Basis differential per MMBtu	(0.44)
Purchased Call Options - 2020 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	68
Cap price per MMBtu	3.63
Fair Value | $	$ 3
Purchased Call Options - 2021 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	57
Cap price per MMBtu	3.52
Fair Value | $	$ 3
Purchased Call Options [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	125
Fair Value | $	$ 6
Sold Call Options - 2018 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	31
Cap price per MMBtu	3.50
Sold Call Options - 2018 [Member] | Oil [Member]
Derivative [Line Items]
Volume | ft³	552
Cap price per MMBtu	65.00
Fair Value | $	$ (5)
Sold Call Options - 2019 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	52
Cap price per MMBtu	3.50
Fair Value | $	$ (3)
Sold Call Options - 2019 [Member] | Oil [Member]
Derivative [Line Items]
Volume | ft³	270
Cap price per MMBtu	65.00
Fair Value | $	$ (2)
Sold Call Options - 2020 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	137
Cap price per MMBtu	3.39
Fair Value | $	$ (10)
Sold Call Options - 2021 [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	114
Cap price per MMBtu	3.33
Fair Value | $	$ (8)
Sold Call Options [Member] | Natural Gas [Member]
Derivative [Line Items]
Volume | ft³	334
Fair Value | $	$ (21)
Sold Call Options [Member] | Oil [Member]
Derivative [Line Items]
Volume | ft³	822
Fair Value | $	$ (7)