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Derivatives and Hedging (Notional Amounts of Derivative Instruments) (Details) Mcf in Millions, $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 USD ($) GWh Mcf | Dec. 31, 2017 USD ($) GWh Mcf
Commodity Contracts [Member] | Electricity [Member] |  |
Derivative [Line Items] |  |
Notional amount, energy measure (in gigawatt-hours) | GWh | 170 | 34
Commodity Contracts [Member] | Natural Gas [Member] |  |
Derivative [Line Items] |  |
Notional amount, volume (in millions of decatherms) | Mcf | 744 | 770
Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 1,538 | $ 1,587
Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | 411 | 660
Not Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | 1,127 | 927
Variable Interest Entity, Primary Beneficiary [Member] | Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | 411 | $ 660
Variable Interest Entity, Primary Beneficiary [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 200 |
Duke Energy Carolinas [Member] | Commodity Contracts [Member] | Natural Gas [Member] |  |
Derivative [Line Items] |  |
Notional amount, volume (in millions of decatherms) | Mcf | 119 | 105
Duke Energy Carolinas [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 400 | $ 400
Duke Energy Carolinas [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 400 | $ 400
Progress Energy [Member] | Commodity Contracts [Member] | Natural Gas [Member] |  |
Derivative [Line Items] |  |
Notional amount, volume (in millions of decatherms) | Mcf | 167 | 183
Progress Energy [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 500 | $ 500
Progress Energy [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 500 | $ 500
Duke Energy Progress [Member] | Commodity Contracts [Member] | Natural Gas [Member] |  |
Derivative [Line Items] |  |
Notional amount, volume (in millions of decatherms) | Mcf | 158 | 133
Duke Energy Progress [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 250 | $ 250
Duke Energy Progress [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 250 | $ 250
Duke Energy Florida [Member] | Commodity Contracts [Member] | Natural Gas [Member] |  |
Derivative [Line Items] |  |
Notional amount, volume (in millions of decatherms) | Mcf | 9 | 50
Duke Energy Florida [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 250 | $ 250
Duke Energy Florida [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | 250 | 250
Duke Energy Ohio [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | 27 | 27
Duke Energy Ohio [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Contracts [Member] |  |
Derivative [Line Items] |  |
Notional amount | $ 27 | $ 27
Duke Energy Indiana [Member] | Commodity Contracts [Member] | Electricity [Member] |  |
Derivative [Line Items] |  |
Notional amount, energy measure (in gigawatt-hours) | GWh | 170 | 34
Duke Energy Indiana [Member] | Commodity Contracts [Member] | Natural Gas [Member] |  |
Derivative [Line Items] |  |
Notional amount, volume (in millions of decatherms) | Mcf | 1 | 2
Piedmont Natural Gas [Member] | Commodity Contracts [Member] | Natural Gas [Member] |  |
Derivative [Line Items] |  |
Notional amount, volume (in millions of decatherms) | Mcf | 457 | 480

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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