Investments in Debt and Equity Securities (Realized Gains and Losses)(Details) (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2017 |
Mar. 31, 2016 |
|
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||
| Realized gains | $ 93 | $ 54 |
| Realized losses | 62 | 50 |
| Duke Energy Carolinas [Member] | ||
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||
| Realized gains | 66 | 34 |
| Realized losses | 40 | 37 |
| Progress Energy [Member] | ||
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||
| Realized gains | 27 | 19 |
| Realized losses | 21 | 13 |
| Duke Energy Progress [Member] | ||
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||
| Realized gains | 24 | 15 |
| Realized losses | 19 | 11 |
| Duke Energy Florida [Member] | ||
| Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] | ||
| Realized gains | 3 | 4 |
| Realized losses | $ 2 | $ 2 |