Derivative and Hedging Activities - Derivative Instruments (Details) MMBbls in Millions, Bcf in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) Bcf MMBbls	Dec. 31, 2019 USD ($) Bcf MMBbls
Derivative [Line Items]
Derivative assets (liabilities), at fair value, net	$ 862	$ 130
Energy related derivative
Derivative [Line Items]
Derivative assets (liabilities), at fair value, net	$ 862	$ 130
Energy related derivative | Oil
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	41	34
Derivative assets (liabilities), at fair value, net	$ 717	$ 5
Energy related derivative | Oil | Fixed-price swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	21	24
Derivative assets (liabilities), at fair value, net	$ 640	$ (7)
Energy related derivative | Oil | Call options
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	9	0
Derivative assets (liabilities), at fair value, net	$ (9)	$ 0
Energy related derivative | Oil | Collars
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	1	2
Derivative assets (liabilities), at fair value, net	$ 48	$ 14
Energy related derivative | Oil | Basis protection swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | MMBbls	10	8
Derivative assets (liabilities), at fair value, net	$ 38	$ (2)
Energy related derivative | Natural Gas
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	481	346
Derivative assets (liabilities), at fair value, net	$ 145	$ 125
Energy related derivative | Natural Gas | Fixed-price swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	199	265
Derivative assets (liabilities), at fair value, net	$ 152	$ 125
Energy related derivative | Natural Gas | Call options
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	113	22
Derivative assets (liabilities), at fair value, net	$ (19)	$ 0
Energy related derivative | Natural Gas | Call swaptions
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	29	29
Derivative assets (liabilities), at fair value, net	$ (4)	$ (2)
Energy related derivative | Natural Gas | Put spreads
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	94	0
Derivative assets (liabilities), at fair value, net	$ 15	$ 0
Energy related derivative | Natural Gas | Basis protection swaps
Derivative [Line Items]
Derivative, nonmonetary notional amount, volume | Bcf	46	30
Derivative assets (liabilities), at fair value, net	$ 1	$ 2