Derivative and Hedging Activities - Fair Value of Recurring Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 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	$ 323	$ 282
Commodity contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative asset	347	422
Derivative liability	24	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	323	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	0	7
Derivative assets (liabilities), at fair value, net	0	7
Quoted Prices in Active Markets (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
Quoted Prices in Active Markets (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
Quoted Prices in Active Markets (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	0
Significant Other Observable 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	291	188
Significant Other Observable Inputs (Level 2) | Commodity contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative asset	307	319
Derivative liability	16	131
Significant Other Observable 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	0
Significant Unobservable 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	32	94
Significant Unobservable Inputs (Level 3) | Commodity contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative asset	40	103
Derivative liability	8	16
Derivative assets (liabilities), at fair value, net	32	87	$ (5)	$ (15)
Significant Unobservable 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	0	7
Derivative assets (liabilities), at fair value, net	$ 0	$ 7	$ 0	$ 0