Derivative and Hedging Activities - Derivative Instruments (Details) MMBbls in Millions, $ in Millions, Bcf in Trillions	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) Bcf MMBbls	Dec. 31, 2018 USD ($) Bcf MMBbls
Derivative [Line Items]
Derivative assets (liabilities), at fair value, net	$ 262	$ 282
Energy related derivative
Derivative [Line Items]
Derivative assets (liabilities), at fair value, net	262	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	37	27
Derivative assets (liabilities), at fair value, net	$ 87	$ 260
Energy related derivative | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	697	966
Derivative assets (liabilities), at fair value, net	$ 175	$ 15
Energy related derivative | Fixed-price swaps | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	24	12
Derivative assets (liabilities), at fair value, net	$ 64	$ 157
Energy related derivative | Fixed-price swaps | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	505	623
Derivative assets (liabilities), at fair value, net	$ 176	$ 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	$ 2	$ 1
Energy related derivative | Collars | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	5	8
Derivative assets (liabilities), at fair value, net	$ 27	$ 98
Energy related derivative | Collars | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	18	55
Derivative assets (liabilities), at fair value, net	$ 7	$ (3)
Energy related derivative | Call options | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	33	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	$ (5)
Energy related derivative | Call swaptions | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	106	106
Derivative assets (liabilities), at fair value, net	$ (10)	$ (9)
Energy related derivative | Put options | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	2
Derivative assets (liabilities), at fair value, net	$ (5)
Energy related derivative | Basis protection swaps | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	4	7
Derivative assets (liabilities), at fair value, net	$ 6	$ 5
Energy related derivative | Basis protection swaps | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	20	50
Derivative assets (liabilities), at fair value, net	$ 0	$ 0