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Investments in Debt and Equity Securities (Estimated Fair Value of Investments in Debt and Equity Securities) (Details) - USD ($) $ in Millions | Sep. 30, 2020 | Dec. 31, 2019
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Debt Securities, Available-for-sale |  |
Estimated Fair Value | $ 2,532 |
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 3,662 | $ 3,675
Unrealized Holding Losses | 106 | 57
Estimated Fair Value | 8,914 | 8,562
Duke Energy Carolinas |  |
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 1,232 |
Progress Energy |  |
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 1,045 |
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 1,482 | 1,655
Unrealized Holding Losses | 52 | 47
Estimated Fair Value | 4,027 | 3,883
Duke Energy Progress |  |
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 992 |
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 1,409 | 1,300
Unrealized Holding Losses | 52 | 21
Estimated Fair Value | 3,200 | 3,053
Duke Energy Florida |  |
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 53 |
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 73 | 355
Unrealized Holding Losses |  | 26
Estimated Fair Value | 723 | 787
Duke Energy Indiana |  |
Equity Securities, FV-NI |  |
Equity Securities, FV-NI, Accumulated Unrealized Gain | 45 | 43
Equity securities, FV-NI | 84 | 81
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 45 |
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 46 | 44
Unrealized Holding Losses | 1 |
Estimated Fair Value | 130 | 125
NDTF |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 687 | 101
Equity Securities, FV-NI |  |
Equity Securities, FV-NI, Accumulated Unrealized Gain | 3,436 | 3,523
Equity Securities, FV-NI, Accumulated Unrealized Loss | 103 | 55
Equity securities, FV-NI | 5,459 | 5,661
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 2,224 | 2,368
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 3,587 | 3,609
Unrealized Holding Losses | 105 | 57
Estimated Fair Value | 8,370 | 8,130
NDTF | Duke Energy Carolinas |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 42 | 21
Equity Securities, FV-NI |  |
Equity Securities, FV-NI, Accumulated Unrealized Gain | 2,027 | 1,914
Equity Securities, FV-NI, Accumulated Unrealized Loss | 52 | 8
Equity securities, FV-NI | 3,229 | 3,154
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 1,232 | 1,172
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 2,109 | 1,957
Unrealized Holding Losses | 53 | 10
Estimated Fair Value | 4,503 | 4,347
NDTF | Progress Energy |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 645 | 80
Equity Securities, FV-NI |  |
Equity Securities, FV-NI, Accumulated Unrealized Gain | 1,409 | 1,609
Equity Securities, FV-NI, Accumulated Unrealized Loss | 51 | 47
Equity securities, FV-NI | 2,230 | 2,507
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 992 | 1,196
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 1,478 | 1,652
Unrealized Holding Losses | 52 | 47
Estimated Fair Value | 3,867 | 3,783
NDTF | Duke Energy Progress |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 57 | 53
Equity Securities, FV-NI |  |
Equity Securities, FV-NI, Accumulated Unrealized Gain | 1,340 | 1,258
Equity Securities, FV-NI, Accumulated Unrealized Loss | 51 | 21
Equity securities, FV-NI | 2,150 | 2,077
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 992 | 921
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 1,409 | 1,300
Unrealized Holding Losses | 52 | 21
Estimated Fair Value | 3,199 | 3,051
NDTF | Duke Energy Florida |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 588 | 27
Equity Securities, FV-NI |  |
Equity Securities, FV-NI, Accumulated Unrealized Gain | 69 | 351
Equity Securities, FV-NI, Accumulated Unrealized Loss |  | 26
Equity securities, FV-NI | 80 | 430
Debt Securities, Available-for-sale |  |
Estimated Fair Value |  | 275
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 69 | 352
Unrealized Holding Losses |  | 26
Estimated Fair Value | 668 | 732
Other Investments |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 110 | 52
Equity Securities, FV-NI |  |
Equity Securities, FV-NI, Accumulated Unrealized Gain | 60 | 57
Equity securities, FV-NI | 126 | 122
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 308 | 258
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 75 | 66
Unrealized Holding Losses | 1 |
Estimated Fair Value | 544 | 432
Other Investments | Progress Energy |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 107 | 49
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 53 | 51
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 4 | 3
Estimated Fair Value | 160 | 100
Other Investments | Duke Energy Progress |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 1 | 2
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Estimated Fair Value | 1 | 2
Other Investments | Duke Energy Florida |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 2 | 4
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 53 | 51
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract] |  |
Unrealized Holding Gains | 4 | 3
Estimated Fair Value | 55 | 55
Other Investments | Duke Energy Indiana |  |
Available-for-sale Securities |  |
Cash and cash equivalents | 1 |
Equity Securities, FV-NI |  |
Equity securities, FV-NI | 84 | 81
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 45 | 44
Corporate debt securities | Duke Energy Indiana |  |
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 3 | 6
Corporate debt securities | NDTF |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 65 | 37
Gross Unrealized Holding Losses | 1 | 1
Estimated Fair Value | 789 | 603
Corporate debt securities | NDTF | Duke Energy Carolinas |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 42 | 21
Gross Unrealized Holding Losses | 1 | 1
Estimated Fair Value | 507 | 361
Corporate debt securities | NDTF | Progress Energy |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 23 | 16
Estimated Fair Value | 282 | 242
Corporate debt securities | NDTF | Duke Energy Progress |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 23 | 16
Estimated Fair Value | 282 | 242
Corporate debt securities | Other Investments |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 8 | 3
Estimated Fair Value | 129 | 67
Municipal bonds | Duke Energy Indiana |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 1 | 1
Gross Unrealized Holding Losses | 1 |
Estimated Fair Value | 39 | 36
Municipal bonds | NDTF |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 19 | 13
Gross Unrealized Holding Losses | 1 |
Estimated Fair Value | 407 | 368
Municipal bonds | NDTF | Duke Energy Carolinas |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 5 | 3
Estimated Fair Value | 118 | 96
Municipal bonds | NDTF | Progress Energy |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 14 | 10
Gross Unrealized Holding Losses | 1 |
Estimated Fair Value | 289 | 272
Municipal bonds | NDTF | Duke Energy Progress |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 14 | 10
Gross Unrealized Holding Losses | 1 |
Estimated Fair Value | 289 | 272
Municipal bonds | Other Investments |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 6 | 4
Gross Unrealized Holding Losses | 1 |
Estimated Fair Value | 114 | 94
Municipal bonds | Other Investments | Progress Energy |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 4 | 3
Estimated Fair Value | 53 | 51
Municipal bonds | Other Investments | Duke Energy Florida |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 4 | 3
Estimated Fair Value | 53 | 51
U.S. government bonds | Duke Energy Indiana |  |
Debt Securities, Available-for-sale |  |
Estimated Fair Value | 3 | 2
U.S. government bonds | NDTF |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 58 | 33
Gross Unrealized Holding Losses |  | 1
Estimated Fair Value | 843 | 1,256
U.S. government bonds | NDTF | Duke Energy Carolinas |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 28 | 16
Gross Unrealized Holding Losses |  | 1
Estimated Fair Value | 428 | 578
U.S. government bonds | NDTF | Progress Energy |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 30 | 17
Estimated Fair Value | 415 | 678
U.S. government bonds | NDTF | Duke Energy Progress |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 30 | 16
Estimated Fair Value | 415 | 403
U.S. government bonds | NDTF | Duke Energy Florida |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains |  | 1
Estimated Fair Value |  | 275
U.S. government bonds | Other Investments |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 1 | 2
Estimated Fair Value | 21 | 41
Other debt securities | NDTF |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 9 | 3
Estimated Fair Value | 185 | 141
Other debt securities | NDTF | Duke Energy Carolinas |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 7 | 3
Estimated Fair Value | 179 | 137
Other debt securities | NDTF | Progress Energy |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 2 |
Estimated Fair Value | 6 | 4
Other debt securities | NDTF | Duke Energy Progress |  |
Debt Securities, Available-for-sale |  |
Gross Unrealized Holding Gains | 2 |
Estimated Fair Value | 6 | 4
Other debt securities | Other Investments |  |
Debt Securities, Available-for-sale |  |
Estimated Fair Value | $ 44 | $ 56

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