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Investments in Debt and Equity Securities (Equity Securities, FV-NI - ASU 2016-01) (Details)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
Sep. 30, 2018
USD ($)
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity securities, FV-NI, realized gain $ 19 $ 85
Equity securities, FV-NI, realized loss 16 60
Ndtf [Member]    
Equity Securities, FV-NI, Accumulated Unrealized Gain (Loss) [Abstract]    
Equity securities, FV-NI, unrealized gain 3,117 3,117
Equity securities, FV-NI, unrealized loss 48 48
Equity securities, FV-NI 5,272 5,272
Other Classification [Member]    
Equity Securities, FV-NI, Accumulated Unrealized Gain (Loss) [Abstract]    
Equity securities, FV-NI, unrealized gain 51 51
Equity securities, FV-NI 115 115
Duke Energy Carolinas [Member]    
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity securities, FV-NI, realized gain 11 47
Equity securities, FV-NI, realized loss 8 30
Duke Energy Carolinas [Member] | Ndtf [Member]    
Equity Securities, FV-NI, Accumulated Unrealized Gain (Loss) [Abstract]    
Equity securities, FV-NI, unrealized gain 1,692 1,692
Equity securities, FV-NI, unrealized loss 29 29
Equity securities, FV-NI 2,890 2,890
Progress Energy [Member]    
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity securities, FV-NI, realized gain 8 38
Equity securities, FV-NI, realized loss 8 30
Progress Energy [Member] | Ndtf [Member]    
Equity Securities, FV-NI, Accumulated Unrealized Gain (Loss) [Abstract]    
Equity securities, FV-NI, unrealized gain 1,425 1,425
Equity securities, FV-NI, unrealized loss 19 19
Equity securities, FV-NI 2,382 2,382
Duke Energy Progress [Member]    
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity securities, FV-NI, realized gain 7 32
Equity securities, FV-NI, realized loss 7 27
Duke Energy Progress [Member] | Ndtf [Member]    
Equity Securities, FV-NI, Accumulated Unrealized Gain (Loss) [Abstract]    
Equity securities, FV-NI, unrealized gain 1,101 1,101
Equity securities, FV-NI, unrealized loss 14 14
Equity securities, FV-NI 1,913 1,913
Duke Energy Florida [Member]    
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity securities, FV-NI, realized gain 1 6
Equity securities, FV-NI, realized loss 1 3
Duke Energy Florida [Member] | Ndtf [Member]    
Equity Securities, FV-NI, Accumulated Unrealized Gain (Loss) [Abstract]    
Equity securities, FV-NI, unrealized gain 324 324
Equity securities, FV-NI, unrealized loss 5 5
Equity securities, FV-NI 469 469
Duke Energy Indiana [Member]    
Equity Securities, FV-NI, Accumulated Unrealized Gain (Loss) [Abstract]    
Equity securities, FV-NI, unrealized gain 40 40
Equity securities, FV-NI 78 78
Duke Energy Indiana [Member] | Other Classification [Member]    
Equity Securities, FV-NI, Accumulated Unrealized Gain (Loss) [Abstract]    
Equity securities, FV-NI $ 78 $ 78