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Investments in Debt and Equity Securities (Realized Gains and Losses) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
FV-NI: |  |  |
Realized gains | $ 168 |  |
Realized losses | 126 |  |
AFS: |  |  |
Realized gains | 22 |  |
Realized losses | 51 |  |
Available-for-sale Securities, Realized Gain (Loss) [Abstract] |  |  |
Realized gains |  | $ 202 | $ 246
Realized losses |  | 160 | 187
Duke Energy Carolinas [Member] |  |  |
FV-NI: |  |  |
Realized gains | 89 |  |
Realized losses | 73 |  |
AFS: |  |  |
Realized gains | 19 |  |
Realized losses | 35 |  |
Available-for-sale Securities, Realized Gain (Loss) [Abstract] |  |  |
Realized gains |  | 135 | 157
Realized losses |  | 103 | 121
Progress Energy [Member] |  |  |
FV-NI: |  |  |
Realized gains | 79 |  |
Realized losses | 53 |  |
AFS: |  |  |
Realized gains | 3 |  |
Realized losses | 15 |  |
Available-for-sale Securities, Realized Gain (Loss) [Abstract] |  |  |
Realized gains |  | 65 | 84
Realized losses |  | 56 | 64
Duke Energy Progress [Member] |  |  |
FV-NI: |  |  |
Realized gains | 68 |  |
Realized losses | 48 |  |
AFS: |  |  |
Realized gains | 2 |  |
Realized losses | 10 |  |
Available-for-sale Securities, Realized Gain (Loss) [Abstract] |  |  |
Realized gains |  | 54 | 71
Realized losses |  | 48 | 55
Duke Energy Florida [Member] |  |  |
FV-NI: |  |  |
Realized gains | 11 |  |
Realized losses | 5 |  |
AFS: |  |  |
Realized gains | 1 |  |
Realized losses | $ 5 |  |
Available-for-sale Securities, Realized Gain (Loss) [Abstract] |  |  |
Realized gains |  | 11 | 13
Realized losses |  | $ 8 | $ 9

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- Definition Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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- Definition Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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