Investments in Debt and Equity Securities (Realized Gains and Losses)(Details) (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2015 |
Sep. 30, 2014 |
Sep. 30, 2015 |
Sep. 30, 2014 |
|
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | $ 30 | $ 28 | $ 160 | $ 90 |
| Realized losses | 28 | 51 | 59 | 57 |
| Duke Energy Carolinas [Member] | ||||
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | 25 | 20 | 132 | 72 |
| Realized losses | 24 | 48 | 47 | 50 |
| Progress Energy [Member] | ||||
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | 5 | 8 | 26 | 17 |
| Realized losses | 4 | 3 | 10 | 6 |
| Duke Energy Progress [Member] | ||||
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | 4 | 4 | 21 | 11 |
| Realized losses | 3 | 2 | 8 | 4 |
| Duke Energy Florida [Member] | ||||
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||||
| Realized gains | 1 | 3 | 5 | 5 |
| Realized losses | $ 1 | $ 1 | $ 2 | $ 2 |