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Investments in Debt and Equity Securities (Equity Securities, FV-NI - ASU 2016-01) (Details)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
Jun. 30, 2018
USD ($)
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity Securities, FV-NI, Realized Gain $ 47 $ 66
Equity Securities, FV-NI, Realized Loss 31 44
Ndtf [Member]    
EquitySecuritiesFvNiAccumulatedUnrealizedGainLoss [Abstract]    
Equity Securities, FV-NI, Unrealized Gain 2,837 2,837
Equity Securities, FV-NI, Unrealized Loss 40 40
Equity Securities, FV-NI 4,988 4,988
Other Classification [Member]    
EquitySecuritiesFvNiAccumulatedUnrealizedGainLoss [Abstract]    
Equity Securities, FV-NI, Unrealized Gain 46 46
Equity Securities, FV-NI 109 109
Duke Energy Carolinas [Member]    
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity Securities, FV-NI, Realized Gain 26 36
Equity Securities, FV-NI, Realized Loss 17 22
Duke Energy Carolinas [Member] | Ndtf [Member]    
EquitySecuritiesFvNiAccumulatedUnrealizedGainLoss [Abstract]    
Equity Securities, FV-NI, Unrealized Gain 1,544 1,544
Equity Securities, FV-NI, Unrealized Loss 23 23
Equity Securities, FV-NI 2,732 2,732
Progress Energy [Member]    
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity Securities, FV-NI, Realized Gain 21 30
Equity Securities, FV-NI, Realized Loss 14 22
Progress Energy [Member] | Ndtf [Member]    
EquitySecuritiesFvNiAccumulatedUnrealizedGainLoss [Abstract]    
Equity Securities, FV-NI, Unrealized Gain 1,293 1,293
Equity Securities, FV-NI, Unrealized Loss 17 17
Equity Securities, FV-NI 2,256 2,256
Duke Energy Progress [Member]    
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity Securities, FV-NI, Realized Gain 17 25
Equity Securities, FV-NI, Realized Loss 12 20
Duke Energy Progress [Member] | Ndtf [Member]    
EquitySecuritiesFvNiAccumulatedUnrealizedGainLoss [Abstract]    
Equity Securities, FV-NI, Unrealized Gain 995 995
Equity Securities, FV-NI, Unrealized Loss 13 13
Equity Securities, FV-NI 1,819 1,819
Duke Energy Florida [Member]    
Equity Securities, FV-NI, Realized Gain (Loss) [Abstract]    
Equity Securities, FV-NI, Realized Gain 4 5
Equity Securities, FV-NI, Realized Loss 2 2
Duke Energy Florida [Member] | Ndtf [Member]    
EquitySecuritiesFvNiAccumulatedUnrealizedGainLoss [Abstract]    
Equity Securities, FV-NI, Unrealized Gain 298 298
Equity Securities, FV-NI, Unrealized Loss 4 4
Equity Securities, FV-NI 437 437
Duke Energy Indiana [Member]    
EquitySecuritiesFvNiAccumulatedUnrealizedGainLoss [Abstract]    
Equity Securities, FV-NI, Unrealized Gain 36 36
Equity Securities, FV-NI 74 74
Duke Energy Indiana [Member] | Other Classification [Member]    
EquitySecuritiesFvNiAccumulatedUnrealizedGainLoss [Abstract]    
Equity Securities, FV-NI $ 74 $ 74