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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, 2020 | Dec. 31, 2019 | Dec. 31, 2018
FV-NI: |  |  |
Realized gains | $ 366 | $ 172 | $ 168
Realized losses | 174 | 151 | 126
AFS: |  |  |
Realized gains | 96 | 94 | 22
Realized losses | 51 | 67 | 51
Duke Energy Carolinas |  |  |
FV-NI: |  |  |
Realized gains | 64 | 113 | 89
Realized losses | 99 | 107 | 73
AFS: |  |  |
Realized gains | 60 | 55 | 19
Realized losses | 37 | 38 | 35
Progress Energy |  |  |
FV-NI: |  |  |
Realized gains | 302 | 59 | 79
Realized losses | 75 | 44 | 53
AFS: |  |  |
Realized gains | 24 | 36 | 3
Realized losses | 13 | 29 | 15
Duke Energy Progress |  |  |
FV-NI: |  |  |
Realized gains | 52 | 38 | 68
Realized losses | 59 | 33 | 48
AFS: |  |  |
Realized gains | 24 | 7 | 2
Realized losses | 13 | 5 | 10
Duke Energy Florida |  |  |
FV-NI: |  |  |
Realized gains | 250 | 21 | 11
Realized losses | 16 | 11 | 5
AFS: |  |  |
Realized gains | 0 | 29 | 1
Realized losses | $ 0 | $ 24 | $ 5

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