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Summary of Significant Accounting Policies (Inventory) (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Public Utilities, Inventory [Line Items] |  |
Materials and supplies | $ 2,238 | $ 2,293
Coal | 491 | 603
Natural gas, oil, other | 355 | 354
Total inventory | 3,084 | 3,250
Duke Energy Carolinas [Member] |  |
Public Utilities, Inventory [Line Items] |  |
Materials and supplies | 731 | 744
Coal | 175 | 192
Natural gas, oil, other | 42 | 35
Total inventory | 948 | 971
Progress Energy [Member] |  |
Public Utilities, Inventory [Line Items] |  |
Materials and supplies | 1,049 | 1,118
Coal | 192 | 255
Natural gas, oil, other | 218 | 219
Total inventory | 1,459 | 1,592
Duke Energy Progress [Member] |  |
Public Utilities, Inventory [Line Items] |  |
Materials and supplies | 734 | 774
Coal | 106 | 139
Natural gas, oil, other | 114 | 104
Total inventory | 954 | 1,017
Duke Energy Florida [Member] |  |
Public Utilities, Inventory [Line Items] |  |
Materials and supplies | 315 | 343
Coal | 86 | 116
Natural gas, oil, other | 103 | 115
Total inventory | 504 | 574
Duke Energy Ohio [Member] |  |
Public Utilities, Inventory [Line Items] |  |
Materials and supplies | 84 | 82
Coal | 14 | 17
Natural gas, oil, other | 28 | 34
Total inventory | 126 | 133
Duke Energy Indiana [Member] |  |
Public Utilities, Inventory [Line Items] |  |
Materials and supplies | 312 | 309
Coal | 109 | 139
Natural gas, oil, other | 1 | 2
Total inventory | 422 | 450
Piedmont Natural Gas [Member] |  |
Public Utilities, Inventory [Line Items] |  |
Materials and supplies | 2 | 2
Natural gas, oil, other | 68 | 64
Total inventory | $ 70 | $ 66

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