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Fair Value Measurements (Reconciliation of Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs) (Details) - USD ($) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Fair Value Measurement Transfers Between Activity Levels | $ 0 | $ 0 | $ 0 | $ 0
Derivatives (net) |  |  |  |
Beginning balance | (124,000,000) | (135,000,000) | (114,000,000) | (166,000,000)
Purchases | 56,000,000 | 55,000,000 | 56,000,000 | 55,000,000
Settlements | (15,000,000) | (9,000,000) | (29,000,000) | (18,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet | (14,000,000) | (2,000,000) | (10,000,000) | 38,000,000
Ending balance | (97,000,000) | (91,000,000) | (97,000,000) | (91,000,000)
Investments and Derivatives, Net |  |  |  |
Beginning balance | (124,000,000) | (130,000,000) | (114,000,000) | (161,000,000)
Total pretax realized or unrealized gains included in comprehensive income |  | 1,000,000 |  | 1,000,000
Purchases | 56,000,000 | 55,000,000 | 56,000,000 | 55,000,000
Sales |  | (6,000,000) |  | (6,000,000)
Settlements | (15,000,000) | (9,000,000) | (29,000,000) | (18,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet | (14,000,000) | (2,000,000) | (10,000,000) | 38,000,000
Ending balance | (97,000,000) | (91,000,000) | (97,000,000) | (91,000,000)
Investments [Member] |  |  |  |
Investments |  |  |  |
Beginning balance |  | 5,000,000 |  | 5,000,000
Total pretax realized or unrealized gains included in comprehensive income |  | 1,000,000 |  | 1,000,000
Sales |  | (6,000,000) |  | (6,000,000)
Duke Energy Carolinas [Member] | Investments [Member] |  |  |  |
Investments |  |  |  |
Beginning balance |  | 3,000,000 |  | 3,000,000
Total pretax realized or unrealized gains included in comprehensive income |  | 1,000,000 |  | 1,000,000
Sales |  | (4,000,000) |  | (4,000,000)
Duke Energy Ohio [Member] |  |  |  |
Derivatives (net) |  |  |  |
Beginning balance | 1,000,000 | 1,000,000 | 1,000,000 | 5,000,000
Purchases | 7,000,000 | 3,000,000 | 7,000,000 | 3,000,000
Settlements | (1,000,000) | (1,000,000) | (1,000,000) | (2,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet | 2,000,000 |  | 2,000,000 | (3,000,000)
Ending balance | 9,000,000 | 3,000,000 | 9,000,000 | 3,000,000
Duke Energy Indiana [Member] |  |  |  |
Derivatives (net) |  |  |  |
Beginning balance | 7,000,000 | 9,000,000 | 27,000,000 | 16,000,000
Purchases | 49,000,000 | 52,000,000 | 49,000,000 | 52,000,000
Settlements | (14,000,000) | (9,000,000) | (28,000,000) | (16,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet | 2,000,000 | (1,000,000) | (4,000,000) | (1,000,000)
Ending balance | 44,000,000 | 51,000,000 | 44,000,000 | 51,000,000
Piedmont Natural Gas [Member] |  |  |  |
Derivatives (net) |  |  |  |
Beginning balance | (132,000,000) | (145,000,000) | (142,000,000) | (187,000,000)
Total gains (losses) and settlements | (18,000,000) |  | (8,000,000) | 42,000,000
Ending balance | $ (150,000,000) | $ (145,000,000) | $ (150,000,000) | $ (145,000,000)

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