Derivative and Hedging Activities - Fair Value of Recurring Assets and Liabilities Table (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative assets (liabilities), at fair value, net	$ (3)	$ 282
Commodity contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset	116	422
Derivative Liability	(126)	(147)
Energy related derivative
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative assets (liabilities), at fair value, net	(3)	282
Energy related derivative | Future Natural Gas Prices | Utica Shale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset		7
Derivative assets (liabilities), at fair value, net	7	7
Fair Value, Inputs, Level 1
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative assets (liabilities), at fair value, net	0	0
Fair Value, Inputs, Level 1 | Commodity contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset	0	0
Derivative Liability	0	0
Fair Value, Inputs, Level 1 | Energy related derivative | Future Natural Gas Prices | Utica Shale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset		0
Fair Value, Inputs, Level 2
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative assets (liabilities), at fair value, net	(13)	188
Fair Value, Inputs, Level 2 | Commodity contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset	89	319
Derivative Liability	(102)	(131)
Fair Value, Inputs, Level 2 | Energy related derivative | Future Natural Gas Prices | Utica Shale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset		0
Fair Value, Inputs, Level 3
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative assets (liabilities), at fair value, net	10	94
Fair Value, Inputs, Level 3 | Commodity contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset	27	103
Derivative Liability	(24)	(16)
Derivative assets (liabilities), at fair value, net	3	87	$ (24)	$ (15)
Fair Value, Inputs, Level 3 | Energy related derivative | Future Natural Gas Prices | Utica Shale
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative Asset		7
Derivative assets (liabilities), at fair value, net	$ 7	$ 7	$ 0	$ 0