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Investments in Debt and Equity Securities (Available-For-Sale Investments) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2017 | Sep. 30, 2017 | Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | $ 2,899
Gross Unrealized Holding Losses |  |  | 42
Estimated Fair Value |  |  | 7,451
Realized Gains | $ 37 | $ 170 |
Realized Losses | 25 | 124 |
Ndtf [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 2,837
Gross Unrealized Holding Losses |  |  | 40
Estimated Fair Value |  |  | 7,088
Ndtf [Member] | Cash and Cash Equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 115
Ndtf [Member] | Equity Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 2,805
Gross Unrealized Holding Losses |  |  | 27
Estimated Fair Value |  |  | 4,914
Ndtf [Member] | Corporate debt securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 17
Gross Unrealized Holding Losses |  |  | 2
Estimated Fair Value |  |  | 570
Ndtf [Member] | Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 4
Gross Unrealized Holding Losses |  |  | 3
Estimated Fair Value |  |  | 344
Ndtf [Member] | US treasury and government [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 11
Gross Unrealized Holding Losses |  |  | 7
Estimated Fair Value |  |  | 1,027
Ndtf [Member] | Other debt obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Losses |  |  | 1
Estimated Fair Value |  |  | 118
Other Classification [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 62
Gross Unrealized Holding Losses |  |  | 2
Estimated Fair Value |  |  | 363
Other Classification [Member] | Cash and Cash Equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 15
Other Classification [Member] | Equity Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 59
Estimated Fair Value |  |  | 123
Other Classification [Member] | Corporate debt securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 1
Estimated Fair Value |  |  | 57
Other Classification [Member] | Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 2
Gross Unrealized Holding Losses |  |  | 1
Estimated Fair Value |  |  | 83
Other Classification [Member] | US treasury and government [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 41
Other Classification [Member] | Other debt obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Losses |  |  | 1
Estimated Fair Value |  |  | 44
Duke Energy Carolinas [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Realized Gains | 20 | 110 |
Realized Losses | 13 | 76 |
Duke Energy Carolinas [Member] | Ndtf [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 1,543
Gross Unrealized Holding Losses |  |  | 20
Estimated Fair Value |  |  | 3,758
Duke Energy Carolinas [Member] | Ndtf [Member] | Cash and Cash Equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 32
Duke Energy Carolinas [Member] | Ndtf [Member] | Equity Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 1,531
Gross Unrealized Holding Losses |  |  | 12
Estimated Fair Value |  |  | 2,692
Duke Energy Carolinas [Member] | Ndtf [Member] | Corporate debt securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 9
Gross Unrealized Holding Losses |  |  | 2
Estimated Fair Value |  |  | 359
Duke Energy Carolinas [Member] | Ndtf [Member] | Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Losses |  |  | 1
Estimated Fair Value |  |  | 60
Duke Energy Carolinas [Member] | Ndtf [Member] | US treasury and government [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 3
Gross Unrealized Holding Losses |  |  | 4
Estimated Fair Value |  |  | 503
Duke Energy Carolinas [Member] | Ndtf [Member] | Other debt obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Losses |  |  | 1
Estimated Fair Value |  |  | 112
Progress Energy [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 1,296
Gross Unrealized Holding Losses |  |  | 20
Estimated Fair Value |  |  | 3,389
Realized Gains | 16 | 58 |
Realized Losses | 12 | 47 |
Progress Energy [Member] | Ndtf [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 1,294
Gross Unrealized Holding Losses |  |  | 20
Estimated Fair Value |  |  | 3,330
Progress Energy [Member] | Ndtf [Member] | Cash and Cash Equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 83
Progress Energy [Member] | Ndtf [Member] | Equity Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 1,274
Gross Unrealized Holding Losses |  |  | 15
Estimated Fair Value |  |  | 2,222
Progress Energy [Member] | Ndtf [Member] | Corporate debt securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 8
Estimated Fair Value |  |  | 211
Progress Energy [Member] | Ndtf [Member] | Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 4
Gross Unrealized Holding Losses |  |  | 2
Estimated Fair Value |  |  | 284
Progress Energy [Member] | Ndtf [Member] | US treasury and government [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 8
Gross Unrealized Holding Losses |  |  | 3
Estimated Fair Value |  |  | 524
Progress Energy [Member] | Ndtf [Member] | Other debt obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 6
Progress Energy [Member] | Other Classification [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 2
Estimated Fair Value |  |  | 59
Progress Energy [Member] | Other Classification [Member] | Cash and Cash Equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 12
Progress Energy [Member] | Other Classification [Member] | Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 2
Estimated Fair Value |  |  | 47
Duke Energy Progress [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 995
Gross Unrealized Holding Losses |  |  | 16
Estimated Fair Value |  |  | 2,592
Realized Gains | 14 | 49 |
Realized Losses | 11 | 41 |
Duke Energy Progress [Member] | Ndtf [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 995
Gross Unrealized Holding Losses |  |  | 16
Estimated Fair Value |  |  | 2,591
Duke Energy Progress [Member] | Ndtf [Member] | Cash and Cash Equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 50
Duke Energy Progress [Member] | Ndtf [Member] | Equity Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 980
Gross Unrealized Holding Losses |  |  | 12
Estimated Fair Value |  |  | 1,795
Duke Energy Progress [Member] | Ndtf [Member] | Corporate debt securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 6
Estimated Fair Value |  |  | 149
Duke Energy Progress [Member] | Ndtf [Member] | Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 4
Gross Unrealized Holding Losses |  |  | 2
Estimated Fair Value |  |  | 283
Duke Energy Progress [Member] | Ndtf [Member] | US treasury and government [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 5
Gross Unrealized Holding Losses |  |  | 2
Estimated Fair Value |  |  | 310
Duke Energy Progress [Member] | Ndtf [Member] | Other debt obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 4
Duke Energy Progress [Member] | Other Classification [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 1
Duke Energy Progress [Member] | Other Classification [Member] | Cash and Cash Equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 1
Duke Energy Florida [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 301
Gross Unrealized Holding Losses |  |  | 4
Estimated Fair Value |  |  | 787
Realized Gains | 2 | 9 |
Realized Losses | $ 1 | $ 6 |
Duke Energy Florida [Member] | Ndtf [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 299
Gross Unrealized Holding Losses |  |  | 4
Estimated Fair Value |  |  | 739
Duke Energy Florida [Member] | Ndtf [Member] | Cash and Cash Equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 33
Duke Energy Florida [Member] | Ndtf [Member] | Equity Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 294
Gross Unrealized Holding Losses |  |  | 3
Estimated Fair Value |  |  | 427
Duke Energy Florida [Member] | Ndtf [Member] | Corporate debt securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 2
Estimated Fair Value |  |  | 62
Duke Energy Florida [Member] | Ndtf [Member] | Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 1
Duke Energy Florida [Member] | Ndtf [Member] | US treasury and government [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 3
Gross Unrealized Holding Losses |  |  | 1
Estimated Fair Value |  |  | 214
Duke Energy Florida [Member] | Ndtf [Member] | Other debt obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 2
Duke Energy Florida [Member] | Other Classification [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 2
Estimated Fair Value |  |  | 48
Duke Energy Florida [Member] | Other Classification [Member] | Cash and Cash Equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 1
Duke Energy Florida [Member] | Other Classification [Member] | Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 2
Estimated Fair Value |  |  | 47
Duke Energy Indiana [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 49
Gross Unrealized Holding Losses |  |  | 1
Estimated Fair Value |  |  | 128
Duke Energy Indiana [Member] | Equity Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Gains |  |  | 49
Estimated Fair Value |  |  | 97
Duke Energy Indiana [Member] | Corporate debt securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Estimated Fair Value |  |  | 3
Duke Energy Indiana [Member] | Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Gross Unrealized Holding Losses |  |  | 1
Estimated Fair Value |  |  | $ 28

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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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