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Callaway Energy Center (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Nuclear Waste Matters [Line Items]        
Debt Securities, Available-for-sale, Amortized Cost $ 253      
Cost 420 $ 387    
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents 107 68 $ 52 $ 351
Cash and Cash Equivalents, at Carrying Value 16 10    
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax   323    
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax 16 6    
Fair Value 684 704    
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax 280      
Debt Securities        
Nuclear Waste Matters [Line Items]        
Debt Securities, Available-for-sale, Amortized Cost 253      
Cost   228    
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax 3 5    
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 4 1    
Fair Value 252 232    
Equity Securities        
Nuclear Waste Matters [Line Items]        
Cost   155    
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax 277 318    
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax 12 5    
Fair Value 427 468    
Available-for-sale Equity Securities, Amortized Cost Basis 162      
Cash        
Nuclear Waste Matters [Line Items]        
Cost 3 2    
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents   0    
Cash and Cash Equivalents and Restricted Cash and Cash Equivalents 0 0    
Cash and Cash Equivalents, at Carrying Value 3 2    
Other Debt And Equity Securities        
Nuclear Waste Matters [Line Items]        
Cost 2      
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax   0    
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax 0      
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax   0    
Fair Value 2 $ 2    
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax $ 0