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Employee Benefit Plans (Components of Net Periodic Pension Costs) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Qualified Pension Plan [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | $ 45 | $ 40 | $ 90 | $ 80
Interest cost on projected benefit obligation | 75 | 82 | 150 | 164
Expected return on plan assets | (140) | (136) | (280) | (272)
Amortization of actuarial loss (gain) | 33 | 36 | 66 | 72
Amortization of prior service (credit) cost | (8) | (6) | (16) | (12)
Other |  | 2 |  | 4
Net periodic costs | 5 | 18 | 10 | 36
Qualified Pension Plan [Member] | Duke Energy Carolinas [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 15 | 12 | 30 | 24
Interest cost on projected benefit obligation | 18 | 20 | 36 | 40
Expected return on plan assets | (37) | (36) | (74) | (71)
Amortization of actuarial loss (gain) | 7 | 8 | 14 | 16
Amortization of prior service (credit) cost | (2) | (2) | (4) | (4)
Net periodic costs | 1 | 2 | 2 | 5
Qualified Pension Plan [Member] | Progress Energy [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 13 | 12 | 26 | 24
Interest cost on projected benefit obligation | 22 | 25 | 46 | 50
Expected return on plan assets | (43) | (43) | (88) | (86)
Amortization of actuarial loss (gain) | 11 | 14 | 22 | 28
Amortization of prior service (credit) cost | (1) | (1) | (2) | (2)
Other |  | 1 |  | 2
Net periodic costs | 2 | 8 | 4 | 16
Qualified Pension Plan [Member] | Duke Energy Progress [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 8 | 6 | 15 | 12
Interest cost on projected benefit obligation | 10 | 12 | 21 | 24
Expected return on plan assets | (21) | (21) | (42) | (42)
Amortization of actuarial loss (gain) | 5 | 6 | 10 | 12
Amortization of prior service (credit) cost | (1) |  | (1) |
Other |  | 1 |  | 1
Net periodic costs | 1 | 4 | 3 | 7
Qualified Pension Plan [Member] | Duke Energy Florida [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 6 | 5 | 11 | 10
Interest cost on projected benefit obligation | 12 | 13 | 25 | 26
Expected return on plan assets | (23) | (21) | (46) | (42)
Amortization of actuarial loss (gain) | 6 | 7 | 12 | 14
Amortization of prior service (credit) cost | (1) |  | (1) |
Net periodic costs |  | 4 | 1 | 8
Qualified Pension Plan [Member] | Duke Energy Ohio [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 1 | 1 | 2 | 2
Interest cost on projected benefit obligation | 4 | 5 | 9 | 10
Expected return on plan assets | (7) | (7) | (14) | (14)
Amortization of actuarial loss (gain) | 1 | 1 | 2 | 2
Net periodic costs | (1) |  | (1) |
Qualified Pension Plan [Member] | Duke Energy Indiana [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 3 | 2 | 5 | 4
Interest cost on projected benefit obligation | 6 | 7 | 12 | 14
Expected return on plan assets | (11) | (11) | (21) | (22)
Amortization of actuarial loss (gain) | 2 | 3 | 4 | 6
Net periodic costs |  | 1 |  | 2
Qualified Pension Plan [Member] | Piedmont Natural Gas [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 2 | 3 | 4 | 6
Interest cost on projected benefit obligation | 3 | 3 | 6 | 6
Expected return on plan assets | (6) | (6) | (12) | (12)
Amortization of actuarial loss (gain) | 3 | 3 | 6 | 6
Amortization of prior service (credit) cost | (3) | (1) | (6) | (2)
Other |  | 1 |  | 1
Net periodic costs | (1) | 3 | (2) | 5
Non-Qualified Pension Plan [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 1 |  | 1 |
Interest cost on projected benefit obligation | 3 | 3 | 6 | 6
Amortization of actuarial loss (gain) | 2 | 2 | 4 | 4
Amortization of prior service (credit) cost | (1) |  | (1) |
Net periodic costs | 5 | 5 | 10 | 10
Non-Qualified Pension Plan [Member] | Duke Energy Carolinas [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 1 |  | 1 |
Interest cost on projected benefit obligation |  | 1 |  | 1
Net periodic costs | 1 | 1 | 1 | 1
Non-Qualified Pension Plan [Member] | Progress Energy [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Interest cost on projected benefit obligation | 1 | 1 | 2 | 2
Amortization of actuarial loss (gain) |  | 1 |  | 2
Amortization of prior service (credit) cost |  |  | 1 |
Net periodic costs | 1 | 2 | 3 | 4
Non-Qualified Pension Plan [Member] | Duke Energy Progress [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Interest cost on projected benefit obligation | 1 |  | 1 | 1
Net periodic costs | 1 |  | 1 | 1
Non-Qualified Pension Plan [Member] | Duke Energy Florida [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Interest cost on projected benefit obligation | 1 |  | 1 | 1
Net periodic costs | 1 |  | 1 | 1
Other Post-Retirement Benefit Plans [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 2 | 1 | 3 | 2
Interest cost on projected benefit obligation | 7 | 9 | 14 | 18
Expected return on plan assets | (4) | (4) | (6) | (7)
Amortization of actuarial loss (gain) | 2 | 2 | 3 | 4
Amortization of prior service (credit) cost | (5) | (29) | (10) | (58)
Net periodic costs | 2 | (21) | 4 | (41)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Carolinas [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 1 |  | 1 |
Interest cost on projected benefit obligation | 1 | 2 | 3 | 4
Expected return on plan assets | (2) | (2) | (4) | (4)
Amortization of actuarial loss (gain) | 1 | (1) | 1 | (2)
Amortization of prior service (credit) cost | (1) | (2) | (2) | (4)
Net periodic costs |  | (3) | (1) | (6)
Other Post-Retirement Benefit Plans [Member] | Progress Energy [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Interest cost on projected benefit obligation | 2 | 3 | 6 | 7
Amortization of actuarial loss (gain) | 1 | 5 | 1 | 10
Amortization of prior service (credit) cost | (2) | (21) | (4) | (42)
Net periodic costs | 1 | (13) | 3 | (25)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Progress [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Interest cost on projected benefit obligation | 2 | 2 | 3 | 4
Amortization of actuarial loss (gain) |  | 3 |  | 6
Amortization of prior service (credit) cost |  | (13) |  | (27)
Net periodic costs | 2 | (8) | 3 | (17)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Florida [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Interest cost on projected benefit obligation | 2 | 2 | 3 | 4
Amortization of actuarial loss (gain) |  | 2 |  | 4
Amortization of prior service (credit) cost | (2) | (7) | (3) | (15)
Net periodic costs |  | (3) |  | (7)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Ohio [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Interest cost on projected benefit obligation | 1 |  | 1 |
Amortization of actuarial loss (gain) |  | (1) |  | (1)
Net periodic costs | 1 | $ (1) | 1 | $ (1)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Indiana [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Interest cost on projected benefit obligation | 1 |  | 2 |
Amortization of actuarial loss (gain) | 1 |  | 2 |
Net periodic costs | 2 |  | 4 |
Other Post-Retirement Benefit Plans [Member] | Piedmont Natural Gas [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Amortization of prior service (credit) cost | (1) |  | (1) |
Net periodic costs | $ (1) |  | $ (1) |

X
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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- Definition Amount of cost recognized for passage of time related to defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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