Derivative and Hedging Activities - Derivative Instruments (Details) MMBbls in Millions, $ in Millions, Bcf in Trillions	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) Bcf MMBbls	Dec. 31, 2018 USD ($) Bcf MMBbls
Derivative [Line Items]
Derivative assets (liabilities), at fair value, net	$ 323	$ 282
Energy related derivative
Derivative [Line Items]
Derivative assets (liabilities), at fair value, net	323	282
Energy related derivative | Future Natural Gas Prices | Utica Shale
Derivative [Line Items]
Derivative assets (liabilities), at fair value, net	$ 0	$ 7
Energy related derivative | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	30	27
Derivative assets (liabilities), at fair value, net	$ 186	$ 260
Energy related derivative | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	625	966
Derivative assets (liabilities), at fair value, net	$ 137	$ 15
Energy related derivative | Fixed-price swaps | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	22	12
Derivative assets (liabilities), at fair value, net	$ 152	$ 157
Energy related derivative | Fixed-price swaps | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	383	623
Derivative assets (liabilities), at fair value, net	$ 139	$ 26
Energy related derivative | Three-way collars | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	15	88
Derivative assets (liabilities), at fair value, net	$ 3	$ 1
Energy related derivative | Collars | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	3	8
Derivative assets (liabilities), at fair value, net	$ 33	$ 98
Energy related derivative | Collars | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	9	55
Derivative assets (liabilities), at fair value, net	$ 3	$ (3)
Energy related derivative | Call options | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	28	44
Derivative assets (liabilities), at fair value, net	$ 0	$ 0
Energy related derivative | Call swaptions | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	2
Derivative assets (liabilities), at fair value, net	$ (1)
Energy related derivative | Call swaptions | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	136	106
Derivative assets (liabilities), at fair value, net	$ (7)	$ (9)
Energy related derivative | Put options | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	1
Derivative assets (liabilities), at fair value, net	$ (2)
Energy related derivative | Basis protection swaps | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	2	7
Derivative assets (liabilities), at fair value, net	$ 4	$ 5
Energy related derivative | Basis protection swaps | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	54	50
Derivative assets (liabilities), at fair value, net	$ (1)	$ 0