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Employee Benefit Plans (Components of Net Periodic Pension Costs) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Qualified Pension Plan [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | $ 47 | $ 40 | $ 137 | $ 120
Interest cost on projected benefit obligation | 74 | 82 | 224 | 246
Expected return on plan assets | (140) | (136) | (420) | (408)
Amortization of actuarial loss (gain) | 33 | 36 | 99 | 108
Amortization of prior service (credit) cost | (8) | (6) | (24) | (18)
Other |  | 2 |  | 6
Net periodic costs | 6 | 18 | 16 | 54
Qualified Pension Plan [Member] | Duke Energy Carolinas [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 15 | 12 | 45 | 36
Interest cost on projected benefit obligation | 18 | 20 | 54 | 60
Expected return on plan assets | (37) | (35) | (111) | (106)
Amortization of actuarial loss (gain) | 7 | 8 | 21 | 24
Amortization of prior service (credit) cost | (2) | (2) | (6) | (6)
Net periodic costs | 1 | 3 | 3 | 8
Qualified Pension Plan [Member] | Progress Energy [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 13 | 12 | 39 | 36
Interest cost on projected benefit obligation | 24 | 25 | 70 | 75
Expected return on plan assets | (45) | (43) | (133) | (129)
Amortization of actuarial loss (gain) | 11 | 14 | 33 | 42
Amortization of prior service (credit) cost | (1) | (1) | (3) | (3)
Other |  | 1 |  | 3
Net periodic costs | 2 | 8 | 6 | 24
Qualified Pension Plan [Member] | Duke Energy Progress [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 7 | 6 | 22 | 18
Interest cost on projected benefit obligation | 10 | 12 | 31 | 36
Expected return on plan assets | (21) | (21) | (63) | (63)
Amortization of actuarial loss (gain) | 6 | 6 | 16 | 18
Amortization of prior service (credit) cost |  |  | (1) |
Other |  |  |  | 1
Net periodic costs | 2 | 3 | 5 | 10
Qualified Pension Plan [Member] | Duke Energy Florida [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 5 | 5 | 16 | 15
Interest cost on projected benefit obligation | 13 | 13 | 38 | 39
Expected return on plan assets | (23) | (21) | (69) | (63)
Amortization of actuarial loss (gain) | 6 | 7 | 18 | 21
Amortization of prior service (credit) cost |  |  | (1) |
Net periodic costs | 1 | 4 | 2 | 12
Qualified Pension Plan [Member] | Duke Energy Ohio [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 2 | 1 | 4 | 3
Interest cost on projected benefit obligation | 4 | 4 | 13 | 14
Expected return on plan assets | (7) | (7) | (21) | (21)
Amortization of actuarial loss (gain) | 1 | 1 | 3 | 3
Net periodic costs |  | (1) | (1) | (1)
Qualified Pension Plan [Member] | Duke Energy Indiana [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 2 | 2 | 7 | 6
Interest cost on projected benefit obligation | 6 | 7 | 18 | 21
Expected return on plan assets | (10) | (11) | (31) | (33)
Amortization of actuarial loss (gain) | 2 | 3 | 6 | 9
Net periodic costs |  | 1 |  | 3
Qualified Pension Plan [Member] | Piedmont Natural Gas [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 2 | 3 | 6 | 9
Interest cost on projected benefit obligation | 3 | 3 | 9 | 9
Expected return on plan assets | (6) | (6) | (18) | (18)
Amortization of actuarial loss (gain) | 3 | 3 | 9 | 9
Amortization of prior service (credit) cost | (3) | (1) | (9) | (3)
Other |  |  |  | 1
Net periodic costs | (1) | 2 | (3) | 7
Non-Qualified Pension Plan [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost |  |  | 1 |
Interest cost on projected benefit obligation | 3 | 4 | 9 | 10
Amortization of actuarial loss (gain) | 2 | 2 | 6 | 6
Amortization of prior service (credit) cost |  |  | (1) |
Net periodic costs | 5 | 6 | 15 | 16
Non-Qualified Pension Plan [Member] | Duke Energy Carolinas [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost |  |  | 1 |
Interest cost on projected benefit obligation |  |  |  | 1
Net periodic costs |  |  | 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 | 3 | 3
Amortization of actuarial loss (gain) |  | 1 |  | 3
Amortization of prior service (credit) cost |  |  | 1 |
Net periodic costs | 1 | 2 | 4 | 6
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 | 2
Net periodic costs |  | 1 | 1 | 2
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 | 2
Net periodic costs |  | 1 | 1 | 2
Other Post-Retirement Benefit Plans [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost | 2 | 1 | 5 | 3
Interest cost on projected benefit obligation | 7 | 9 | 21 | 27
Expected return on plan assets | (4) | (3) | (10) | (10)
Amortization of actuarial loss (gain) | 2 | 2 | 5 | 6
Amortization of prior service (credit) cost | (5) | (29) | (15) | (87)
Net periodic costs | 2 | (20) | 6 | (61)
Other Post-Retirement Benefit Plans [Member] | Duke Energy Carolinas [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Service cost |  |  | 1 |
Interest cost on projected benefit obligation | 2 | 2 | 5 | 6
Expected return on plan assets | (2) | (2) | (6) | (6)
Amortization of actuarial loss (gain) | 1 |  | 2 | (2)
Amortization of prior service (credit) cost | (1) | (2) | (3) | (6)
Net periodic costs |  | (2) | (1) | (8)
Other Post-Retirement Benefit Plans [Member] | Progress Energy [Member] |  |  |  |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] |  |  |  |
Interest cost on projected benefit obligation | 3 | 4 | 9 | 11
Amortization of actuarial loss (gain) |  | 5 | 1 | 15
Amortization of prior service (credit) cost | (2) | (21) | (6) | (63)
Net periodic costs | 1 | (12) | 4 | (37)
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 | 5 | 6
Amortization of actuarial loss (gain) |  | 3 |  | 9
Amortization of prior service (credit) cost |  | (14) |  | (41)
Net periodic costs | 2 | (9) | 5 | (26)
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 | 1 | 2 | 4 | 6
Amortization of actuarial loss (gain) |  | 2 |  | 6
Amortization of prior service (credit) cost | (1) | (8) | (4) | (23)
Net periodic costs |  | (4) |  | (11)
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 |
Amortization of actuarial loss (gain) |  |  |  | (1)
Net periodic costs |  |  | 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 | 1 | 3 | 1
Amortization of actuarial loss (gain) | 1 |  | 3 |
Net periodic costs | $ 2 | $ 1 | 6 | $ 1
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) |
Net periodic costs |  |  | $ (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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