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Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Millions | 2 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Oct. 31, 2016 | Jan. 01, 2019
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Impact of plan conversion on next year's net periodic benefit cost |  | $ 33 |  |  |  |
Maximum years of participation |  | 35 years |  |  |  |
Additional contribution percentage for employees not participating in defined pension plans |  | 4.00% |  |  |  |
Master Trust [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Target allocation |  | 100.00% |  |  |  |
Expected long-term rate of return on plan assets |  | 6.85% |  |  |  |
Fair value of securities on loan |  | $ 154 | $ 195 |  |  |
Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 13 years |  |  |  |
Expected long-term rate of return on plan assets |  |  |  | 6.75% |  |
Pension Plan [Member] | Nonqualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 10 years |  |  |  |
Pension Plan [Member] | Master Trust [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Master trust allocation percentage |  | 98.00% |  |  |  |
Other Post-Retirement Benefit Plans [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 9 years |  |  |  |
Expected long-term rate of return on plan assets |  | 6.50% | 6.50% | 6.50% |  |
Other Post-Retirement Benefit Plans [Member] | Master Trust [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Master trust allocation percentage |  | 2.00% |  |  |  |
Duke Energy Carolinas [Member] | Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 12 years |  |  |  |
Duke Energy Carolinas [Member] | Pension Plan [Member] | Nonqualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 8 years |  |  |  |
Duke Energy Carolinas [Member] | Other Post-Retirement Benefit Plans [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 8 years |  |  |  |
Progress Energy [Member] | Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 12 years |  |  |  |
Progress Energy [Member] | Pension Plan [Member] | Nonqualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 13 years |  |  |  |
Progress Energy [Member] | Other Post-Retirement Benefit Plans [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 6 years |  |  |  |
Duke Energy Progress [Member] | Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 13 years |  |  |  |
Duke Energy Progress [Member] | Pension Plan [Member] | Nonqualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 11 years |  |  |  |
Duke Energy Progress [Member] | Other Post-Retirement Benefit Plans [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 6 years |  |  |  |
Duke Energy Florida [Member] | Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 12 years |  |  |  |
Duke Energy Florida [Member] | Pension Plan [Member] | Nonqualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 15 years |  |  |  |
Duke Energy Florida [Member] | Other Post-Retirement Benefit Plans [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 7 years |  |  |  |
Duke Energy Ohio [Member] | Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 14 years |  |  |  |
Duke Energy Ohio [Member] | Pension Plan [Member] | Nonqualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 8 years |  |  |  |
Duke Energy Ohio [Member] | Other Post-Retirement Benefit Plans [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 7 years |  |  |  |
Duke Energy Indiana [Member] | Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 14 years |  |  |  |
Duke Energy Indiana [Member] | Pension Plan [Member] | Nonqualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 8 years |  |  |  |
Duke Energy Indiana [Member] | Other Post-Retirement Benefit Plans [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 6 years |  |  |  |
Piedmont Natural Gas [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Additional contribution percentage for employees not participating in defined pension plans |  | 4.00% |  |  |  |
Vesting period |  | 3 years |  |  |  |
Term |  | 3 years |  |  |  |
Piedmont Natural Gas [Member] | Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 10 years |  |  |  |
Expected long-term rate of return on plan assets | 6.75% |  |  |  | 7.25% |
Piedmont Natural Gas [Member] | Pension Plan [Member] | Nonqualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 8 years |  |  |  |
Piedmont Natural Gas [Member] | Other Post-Retirement Benefit Plans [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Average remaining service period, in years |  | 7 years |  |  |  |
Expected long-term rate of return on plan assets | 6.75% |  |  |  | 7.25% |
Liability Hedging Assets [Member] | Subsequent Event [Member] | Pension Plan [Member] | Master Trust [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Target allocation |  |  |  |  |  | 58.00%
Return Seeking Assets [Member] | Subsequent Event [Member] | Pension Plan [Member] | Master Trust [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Target allocation |  |  |  |  |  | 42.00%
Minimum [Member] | Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Expected long-term rate of return on plan assets |  |  | 6.50% | 6.50% |  |
Minimum [Member] | Piedmont Natural Gas [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Additional contribution percentage for employees not participating in defined pension plans |  | 3.00% |  |  |  |
Maximum [Member] | Pension Plan [Member] | Qualified Plan [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Expected long-term rate of return on plan assets |  | 6.50% | 6.75% |  |  |
Maximum [Member] | Piedmont Natural Gas [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
Additional contribution percentage for employees not participating in defined pension plans |  | 5.00% |  |  |  |

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