Fair Value Measurements (Quantitative Level 3 Fair Value Disclosures) (Details) $ in Millions	Sep. 30, 2020 USD ($) $ / MWh $ / MMBTU	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) $ / MWh $ / MMBTU	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques
Net derivative asset (liability) | $	$ (203)	$ (92)	$ (102)	$ (90)	$ (79)	$ (113)
Electricity contracts | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques
Net derivative asset (liability) | $	$ (102)
Electricity contracts | RTO auction pricing | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu)	14.92
Electricity contracts | RTO auction pricing | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu)	151.18
Electricity contracts | RTO auction pricing | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu)	29.63
Duke Energy Ohio | FTRs | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques
Net derivative asset (liability) | $	$ 2		$ 4
Duke Energy Ohio | FTRs | RTO auction pricing | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu)	0		0.59
Duke Energy Ohio | FTRs | RTO auction pricing | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu)	1.90		3.47
Duke Energy Ohio | FTRs | RTO auction pricing | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu)	0.64		2.07
Duke Energy Indiana
Fair Value Measurement Inputs and Valuation Techniques
Net derivative asset (liability) | $	$ 8	10	$ 11	16	28	22
Duke Energy Indiana | FTRs | RTO auction pricing
Fair Value Measurement Inputs and Valuation Techniques
Net derivative asset (liability) | $	$ 8		$ 11
Duke Energy Indiana | FTRs | RTO auction pricing | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu)	(1.03)		(0.66)
Duke Energy Indiana | FTRs | RTO auction pricing | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu)	6.10		9.24
Duke Energy Indiana | FTRs | RTO auction pricing | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu)	0.74		1.15
Piedmont Natural Gas
Fair Value Measurement Inputs and Valuation Techniques
Net derivative asset (liability) | $	$ (111)	$ (105)	$ (117)	$ (111)	$ (114)	$ (141)
Piedmont Natural Gas | Electricity and natural gas contracts | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques
Net derivative asset (liability) | $	$ (111)		$ (117)
Piedmont Natural Gas | Electricity and natural gas contracts | Discounted cash flow | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu) | $ / MMBTU	1.81		1.59
Piedmont Natural Gas | Electricity and natural gas contracts | Discounted cash flow | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu) | $ / MMBTU	2.50		2.46
Piedmont Natural Gas | Electricity and natural gas contracts | Discounted cash flow | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques
Input measurements (in usd per MWh and usd per MMBtu) | $ / MMBTU	2.11		1.91