Derivative and Hedging Activities - Fair Value of Recurring Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative assets (liabilities), at fair value, net		$ 130
Commodity contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative asset		174
Derivative liability		(44)
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
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
Derivative liability		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		118
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		160
Derivative liability		(42)
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		12
Significant Unobservable Inputs (Level 3) | Commodity contract
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Derivative asset		14
Derivative liability		(2)
Derivative assets (liabilities), at fair value, net	$ 0	$ 12	$ 22	$ 87