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Investments in Debt and Equity Securities (Realized Gains and Losses)(Details) (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
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Sep. 30, 2014
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Sep. 30, 2013
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Sep. 30, 2014
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Sep. 30, 2013
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| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | $ 28 | $ 72 | $ 90 | $ 135 |
| Realized losses | 51 | 16 | 57 | 38 |
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Duke Energy Carolinas [Member]
|
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| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | 20 | 49 | 72 | 95 |
| Realized losses | 48 | 1 | 50 | 11 |
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Progress Energy [Member]
|
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| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | 8 | 22 | 17 | 37 |
| Realized losses | 3 | 11 | 6 | 20 |
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Duke Energy Progress [Member]
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| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | 4 | 7 | 11 | 15 |
| Realized losses | 2 | 2 | 4 | 6 |
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Duke Energy Florida [Member]
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| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | 3 | 14 | 5 | 22 |
| Realized losses | $ 1 | $ 9 | $ 2 | $ 13 |