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New And Significant Accounting Policies (Narrative) (Details) - Asset Retirement Obligation Costs [Member] - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2016
Dec. 31, 2015
Public Utility, Property, Plant and Equipment [Line Items]    
Total nuclear decommissioning asset retirement obligation $ 3,300 $ 2,500
Adjustment to nuclear decommissioning cost estimates 818  
Adjustment to undiscounted nuclear decommissioning cost estimates 1,400  
Total undiscounted nuclear decommissioning cost estimates $ 4,800