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Derivative Assets And Liabilities (Fair Value Of Derivative Instruments) (Details) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Asset Derivatives $ 384 $ 560
Liability Derivatives (788) (746)
Designated as Hedging Instrument [Member]    
Asset Derivatives 24 0
Liability Derivatives 0 (13)
Not Designated as Hedging Instrument [Member]    
Asset Derivatives 360 560
Liability Derivatives (788) (733)
Broker cleared derivative contracts [Member]    
Asset Derivatives 343 402
Liability Derivatives (350) (410)
Commodity Derivatives [Member] | Not Designated as Hedging Instrument [Member]    
Asset Derivatives 41 158
Liability Derivatives (39) (173)
Commodity Derivatives (Margin Deposits) [Member] | Designated as Hedging Instrument [Member]    
Asset Derivatives 24 0
Liability Derivatives 0 (13)
Commodity Derivatives (Margin Deposits) [Member] | Not Designated as Hedging Instrument [Member]    
Asset Derivatives 319 402
Liability Derivatives (350) (397)
Interest Rate Derivatives [Member] | Not Designated as Hedging Instrument [Member]    
Asset Derivatives 0 0
Liability Derivatives $ (399) $ (163)