Fair Value Measurements (Quantitative Level 3 Fair Value Disclosure) (Details) $ in Millions	Dec. 31, 2020 USD ($) $ / MWh	Dec. 31, 2019 USD ($) $ / MWh $ / MMBTU	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative asset (liability) | $	$ (77)	$ (102)	$ (113)
Forward natural gas curves – price per MMBtu | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative asset (liability) | $	$ (84)
Forward natural gas curves – price per MMBtu | Minimum | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu)	14.68
Forward natural gas curves – price per MMBtu | Maximum | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu)	151.84
Forward natural gas curves – price per MMBtu | Weighted Average | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu)	28.84
Duke Energy Ohio | FTR price – per MWh | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative asset (liability) | $	$ 1	$ 4
Duke Energy Ohio | FTR price – per MWh | Minimum | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu)	0.25	0.59
Duke Energy Ohio | FTR price – per MWh | Maximum | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu)	1.68	3.47
Duke Energy Ohio | FTR price – per MWh | Weighted Average | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu)	0.79	2.07
Duke Energy Indiana
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative asset (liability) | $	$ 6	$ 11	22
Duke Energy Indiana | FTR price – per MWh | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative asset (liability) | $	$ 6	$ 11
Duke Energy Indiana | FTR price – per MWh | Minimum | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu)	(2.40)	(0.66)
Duke Energy Indiana | FTR price – per MWh | Maximum | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu)	7.41	9.24
Duke Energy Indiana | FTR price – per MWh | Weighted Average | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu)	1.05	1.15
Piedmont
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative asset (liability) | $	$ 0	$ (117)	$ (141)
Piedmont | Forward natural gas curves – price per MMBtu | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Net derivative asset (liability) | $		$ (117)
Piedmont | Forward natural gas curves – price per MMBtu | Minimum | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu) | $ / MMBTU		1.59
Piedmont | Forward natural gas curves – price per MMBtu | Maximum | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu) | $ / MMBTU		2.46
Piedmont | Forward natural gas curves – price per MMBtu | Weighted Average | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Input measurement (in usd per MWh and usd per MMBtu) | $ / MMBTU		1.91