Risk Management - Fair Value of Derivative Contracts (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Derivatives Assets	$ 1,102	$ 460
Derivatives Liability	(79)	(65)
Energy commodity derivative contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	262	56
Derivatives Liability	(25)	(58)
Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	818	358
Derivatives Liability	(18)	(1)
Foreign currency contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	22	46
Derivatives Liability	(36)	(6)
Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivatives Assets	1,082	452
Derivatives Liability	(67)	(58)
Derivatives designated as hedging instruments | Energy commodity derivative contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	242	48
Derivatives Liability	(19)	(51)
Derivatives designated as hedging instruments | Energy commodity derivative contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	150	31
Derivatives designated as hedging instruments | Energy commodity derivative contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	(17)	(43)
Derivatives designated as hedging instruments | Energy commodity derivative contracts | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivatives Assets	92	17
Derivatives designated as hedging instruments | Energy commodity derivative contracts | Other long-term liabilities and deferred credits
Derivatives, Fair Value [Line Items]
Derivatives Liability	(2)	(8)
Derivatives designated as hedging instruments | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	818	358
Derivatives Liability	(12)	(1)
Derivatives designated as hedging instruments | Interest rate contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	128	45
Derivatives designated as hedging instruments | Interest rate contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	(3)	0
Derivatives designated as hedging instruments | Interest rate contracts | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivatives Assets	690	313
Derivatives designated as hedging instruments | Interest rate contracts | Other long-term liabilities and deferred credits
Derivatives, Fair Value [Line Items]
Derivatives Liability	(9)	(1)
Derivatives designated as hedging instruments | Foreign currency contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	22	46
Derivatives Liability	(36)	(6)
Derivatives designated as hedging instruments | Foreign currency contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	0	0
Derivatives designated as hedging instruments | Foreign currency contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	(22)	(6)
Derivatives designated as hedging instruments | Foreign currency contracts | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivatives Assets	22	46
Derivatives designated as hedging instruments | Foreign currency contracts | Other long-term liabilities and deferred credits
Derivatives, Fair Value [Line Items]
Derivatives Liability	(14)	0
Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivatives Assets	20	8
Derivatives Liability	(12)	(7)
Derivatives not designated as hedging instruments | Energy commodity derivative contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	20	8
Derivatives Liability	(6)	(7)
Derivatives not designated as hedging instruments | Energy commodity derivative contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	16	8
Derivatives not designated as hedging instruments | Energy commodity derivative contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	(5)	(7)
Derivatives not designated as hedging instruments | Energy commodity derivative contracts | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivatives Assets	4	0
Derivatives not designated as hedging instruments | Energy commodity derivative contracts | Other long-term liabilities and deferred credits
Derivatives, Fair Value [Line Items]
Derivatives Liability	(1)	0
Derivatives not designated as hedging instruments | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	0	0
Derivatives Liability	(6)	0
Derivatives not designated as hedging instruments | Interest rate contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Assets	0	0
Derivatives not designated as hedging instruments | Interest rate contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	$ (6)	$ 0