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Investments and Restricted Cash and Cash Equivalents and Investments - MEC (Details) - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]    
Total $ 15,788 $ 14,320
Quad Cities Station nuclear decommissioning trust funds    
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]    
Nuclear decommissioning trust 768 676
MEC    
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]    
Rabbi trusts 233 211
Other 25 24
Total $ 1,026 $ 911
MEC | United States companies    
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]    
Ownership percentage 56.00% 56.00%
MEC | US Government Corporations and Agencies Securities    
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]    
Ownership percentage 30.00% 30.00%
MEC | Corporate obligations    
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]    
Ownership percentage 12.00% 11.00%
MEC | Other    
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]    
Ownership percentage 2.00% 3.00%
MEC | Quad Cities Station nuclear decommissioning trust funds    
Investments, Including Equity Method And Restricted Cash And Investments [Line Items]    
Nuclear decommissioning trust $ 768 $ 676