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Regulatory Matters (Other Regulatory Matters Narrative) (Details) - USD ($) $ in Millions |  | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Sep. 02, 2014 | Dec. 31, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Investments in equity method unconsolidated affiliates |  | $ 1,936 | $ 1,936 | $ 1,409 | $ 1,175
Remaining net book value |  | 102,127 | 102,127 | 91,694 |
Atlantic Coast Pipeline (ACP) |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Joint owner ownership percentage | 47.00% |  |  |  |
Supply contract, term | 20 years |  |  |  |
Estimated capital cost |  | 8,000 | 8,000 |  |
Investments in equity method unconsolidated affiliates |  | 1,200 | 1,200 |  |
Maximum loss exposure, amount |  | $ 827 | $ 827 |  |
Atlantic Coast Pipeline (ACP) | Dominion Resources |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Joint owner ownership percentage | 48.00% |  |  |  |
Atlantic Coast Pipeline (ACP) | Southern Company Gas |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Joint owner ownership percentage | 5.00% |  |  |  |
Constitution |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Joint owner ownership percentage |  | 24.00% | 24.00% |  |
OTTI impairment loss |  | $ 25 |  |  |
Constitution | Williams Partners L.P. |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Joint owner ownership percentage |  | 41.00% | 41.00% |  |
Duke Energy Carolinas |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Remaining net book value |  | $ 32,397 | $ 32,397 | 29,245 |
Duke Energy Carolinas | Atlantic Coast Pipeline (ACP) |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Long-term purchase commitment term | 20 years |  |  |  |
Duke Energy Progress |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Remaining net book value |  | 22,934 | 22,934 | 20,398 |
Duke Energy Progress | Atlantic Coast Pipeline (ACP) |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Long-term purchase commitment term | 20 years |  |  |  |
Piedmont |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Investments in equity method unconsolidated affiliates |  | 83 | 83 | 64 |
Remaining net book value |  | 6,765 | 6,765 | $ 5,911 |
Piedmont | Atlantic Coast Pipeline (ACP) |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Long-term purchase commitment term | 20 years |  |  |  |
Generation Facilities Evaluated For Retirement | Duke Energy Carolinas |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Remaining net book value |  | 721 | 721 |  |
Generation Facilities Evaluated For Retirement | Duke Energy Progress |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Remaining net book value |  | $ 1,200 | $ 1,200 |  |
Financial guarantee | ACP |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
Maximum exposure percentage |  |  | 47.00% |  |

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