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Investments and Restricted Cash and Investments (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Investments [Abstract]      
Investments $ 1,719 $ 1,974  
Gain (Loss) on Investments (288) (538) $ 14
Marketable Securities, Realized Gain (Loss) 2 2  
Marketable Securities, Unrealized Gain (Loss)   (540)  
Equity Method Investments [Abstract]      
Tax Equity Contributions 1,619 698 $ 403
Purchase Obligation, Due in Next Twelve Months 2,400    
Equity method investments 3,947 2,440  
Restricted Cash and Investments [Abstract]      
Restricted cash and investments 829 760  
Investments, including equity method and restricted cash and investments 6,495 5,174  
Investments, including equity method and restricted cash and investments, noncurrent 6,255 4,903  
Investments, including equity method and restricted cash and investments, current 240 271  
Quad Cities Station nuclear decommissioning trust funds [Member]      
Restricted Cash and Investments [Abstract]      
Decommissioning Fund Investments, Fair Value 599 504  
Restricted Cash and Investments, Other [Member]      
Restricted Cash and Investments [Abstract]      
Restricted cash and investments 230 256  
Electric Transmission Texas, LLC [Member]      
Equity Method Investments [Abstract]      
Equity method investments $ 555 527  
Equity method investment, ownership percentage 50.00%    
Bridger Coal Company [Member]      
Equity Method Investments [Abstract]      
Equity method investments $ 81 99  
Equity method investment, ownership percentage 66.67%    
Tax Equity Investments      
Equity Method Investments [Abstract]      
Equity method investments $ 3,130 1,661  
Other equity method investments [Member]      
Equity Method Investments [Abstract]      
Equity method investments 181 153  
BYD Company Limited common stock [Member]      
Investments [Abstract]      
Available-for-sale Securities, Equity Securities 1,122 1,435  
Rabbi trusts [Member]      
Investments [Abstract]      
Life Insurance, Corporate or Bank Owned, Amount 410 371  
Other investments [Member]      
Investments [Abstract]      
Other Investments $ 187 $ 168