Risk Management - Fair Value of Derivative Contracts (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Derivatives Asset	$ 575	$ 931
Derivatives Liability	(443)	(78)
Energy commodity derivative contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	28	99
Derivatives Liability	(418)	(63)
Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	478	694
Derivatives Liability	(19)	(10)
Foreign currency contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	69	138
Derivatives Liability	(6)	(6)
Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivatives Asset	560	907
Derivatives Liability	(376)	(57)
Derivatives designated as hedging instruments | Energy commodity derivative contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	14	75
Derivatives Liability	(352)	(41)
Derivatives designated as hedging instruments | Energy commodity derivative contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	13	42
Derivatives designated as hedging instruments | Energy commodity derivative contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	(256)	(33)
Derivatives designated as hedging instruments | Energy commodity derivative contracts | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivatives Asset	1	33
Derivatives designated as hedging instruments | Energy commodity derivative contracts | Other long-term liabilities and deferred credits
Derivatives, Fair Value [Line Items]
Derivatives Liability	(96)	(8)
Derivatives designated as hedging instruments | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	477	694
Derivatives Liability	(18)	(10)
Derivatives designated as hedging instruments | Interest rate contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	127	119
Derivatives designated as hedging instruments | Interest rate contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	(4)	(3)
Derivatives designated as hedging instruments | Interest rate contracts | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivatives Asset	350	575
Derivatives designated as hedging instruments | Interest rate contracts | Other long-term liabilities and deferred credits
Derivatives, Fair Value [Line Items]
Derivatives Liability	(14)	(7)
Derivatives designated as hedging instruments | Foreign currency contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	69	138
Derivatives Liability	(6)	(6)
Derivatives designated as hedging instruments | Foreign currency contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	49	0
Derivatives designated as hedging instruments | Foreign currency contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	(6)	(6)
Derivatives designated as hedging instruments | Foreign currency contracts | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivatives Asset	20	138
Derivatives designated as hedging instruments | Foreign currency contracts | Other long-term liabilities and deferred credits
Derivatives, Fair Value [Line Items]
Derivatives Liability	0	0
Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Derivatives Asset	15	24
Derivatives Liability	(67)	(21)
Derivatives not designated as hedging instruments | Energy commodity derivative contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	14	24
Derivatives Liability	(66)	(21)
Derivatives not designated as hedging instruments | Energy commodity derivative contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	10	24
Derivatives not designated as hedging instruments | Energy commodity derivative contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	(63)	(21)
Derivatives not designated as hedging instruments | Energy commodity derivative contracts | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivatives Asset	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	(3)	0
Derivatives not designated as hedging instruments | Interest rate contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	1	0
Derivatives Liability	(1)	0
Derivatives not designated as hedging instruments | Interest rate contracts | Fair value of derivatives contracts
Derivatives, Fair Value [Line Items]
Derivatives Asset	0	0
Derivatives not designated as hedging instruments | Interest rate contracts | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivatives Liability	(1)	0
Derivatives not designated as hedging instruments | Interest rate contracts | Deferred charges and other assets
Derivatives, Fair Value [Line Items]
Derivatives Asset	1	0
Derivatives not designated as hedging instruments | Interest rate contracts | Other long-term liabilities and deferred credits
Derivatives, Fair Value [Line Items]
Derivatives Liability	$ 0	$ 0