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Regulatory Matters (Regulatory Matters Narrative - Duke Energy Ohio) (Details)
$ in Millions
1 Months Ended 9 Months Ended
Oct. 16, 2020
USD ($)
Apr. 27, 2020
USD ($)
Jan. 31, 2020
USD ($)
Sep. 03, 2019
USD ($)
Apr. 13, 2018
USD ($)
Mar. 31, 2017
USD ($)
Sep. 30, 2020
USD ($)
site
Jul. 23, 2020
USD ($)
Mar. 31, 2020
USD ($)
Jul. 12, 2019
USD ($)
Mar. 29, 2019
USD ($)
Sep. 28, 2018
USD ($)
Duke Energy Ohio | Ohio Base Rate Case 2017 | PUCO                        
Public Utilities, General Disclosures [Line Items]                        
Requested rate increase (decrease), amount           $ 15            
Requested return on equity, percent           10.40%            
Requested rate increase (decrease), amended amount         $ (19)              
Requested rate increase (decrease) amended, percentage         9.84%              
Public utilities, requested equity capital structure, percentage         50.75%              
Public utilities, requested debt capital structure, percentage         49.25%              
Approved rate increase (decrease), amount         $ (20)              
Duke Energy Ohio | Ohio Base Rate Case 2017 | PUCO | Maximum                        
Public Utilities, General Disclosures [Line Items]                        
Requested rider revenue increase         $ 10              
Duke Energy Ohio | Natural Gas Pipeline extension | OPSB | Minimum                        
Public Utilities, General Disclosures [Line Items]                        
Estimated capital cost excluding AFUDC             $ 163          
Duke Energy Ohio | Natural Gas Pipeline extension | OPSB | Maximum                        
Public Utilities, General Disclosures [Line Items]                        
Estimated capital cost excluding AFUDC             $ 245          
Duke Energy Ohio | MGP Cost Recovery - 2009 Through 2012 | PUCO                        
Public Utilities, General Disclosures [Line Items]                        
Number of environmental remediation sites | site             2          
Regulatory assets             $ 55          
Duke Energy Ohio | MGP Cost Recovery - 2013 Through 2017 | PUCO                        
Public Utilities, General Disclosures [Line Items]                        
Regulatory assets                       $ 26
Duke Energy Ohio | MGP Cost Recovery - 2013 Through 2017 | PUCO | MGP Costs - regulatory disallowance                        
Public Utilities, General Disclosures [Line Items]                        
Regulatory assets                       $ 12
Duke Energy Ohio | MGP Cost Recovery - 2018 | PUCO                        
Public Utilities, General Disclosures [Line Items]                        
Regulatory assets                     $ 20  
Duke Energy Ohio | MGP Cost Recovery - 2018 | PUCO | MGP Costs - regulatory disallowance                        
Public Utilities, General Disclosures [Line Items]                        
Regulatory assets                   $ 11    
Duke Energy Ohio | MGP Cost Recovery - 2019 | PUCO                        
Public Utilities, General Disclosures [Line Items]                        
Regulatory assets               $ 4 $ 39      
Duke Energy Kentucky | Duke Energy Kentucky Electric base rate case | KPSC                        
Public Utilities, General Disclosures [Line Items]                        
Requested rate increase (decrease), amount       $ 46                
Requested rate increase (decrease), amended amount     $ 44                  
Approved rate increase (decrease), amount   $ 24                    
Approved return on equity percentage   9.25%                    
Duke Energy Kentucky | Duke Energy Kentucky Electric base rate case | KPSC | Subsequent event                        
Public Utilities, General Disclosures [Line Items]                        
Approved rate increase (decrease), amount $ 28                      
Approved additional increase $ 4