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Regulatory Matters (Regulatory Matters Narrative - Duke Energy Indiana) (Details) - Duke Energy Indiana - IURC - Indiana rate case 2019 - USD ($)
$ in Millions
Jul. 28, 2021
Jun. 29, 2020
Dec. 04, 2019
Jul. 02, 2019
Public Utilities, General Disclosures [Line Items]        
Requested rate increase (decrease), amount       $ 395
Requested rate increase, percentage, net of tax     15.60%  
Requested rate increase (decrease), amended amount     $ 396  
Approved rate increase, amount   $ 146    
Rate base   10,200    
Reduction of requested rate increase   $ 200    
Reduction due to depreciation methodology   50.00%    
Reduction due to approved return on equity   20.00%    
Requested return on equity, percent   10.40%    
Reduction due to earnings adjustments   20.00%    
Estimated percentage of total rate increase, step one   75.00%    
Estimated percentage of total rate increase, step two   25.00%    
Approved return on equity percentage   9.70%    
Subsequent event        
Public Utilities, General Disclosures [Line Items]        
Approved return on equity percentage 9.70%      
Public utilities, approved equity capital structure, percentage 54.00%