Fair Value Measurements (Quantitative Level 3 Fair Value Disclosure) (Details) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($) $ / MWh	Dec. 31, 2014 USD ($) $ / MWh $ / MMBTU $ / MW
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)	$ 17	$ (1)
Commodity Natural Gas Hedges [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)		$ (5)
Commodity Natural Gas Hedges [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair Value Inputs Price Per MMBtu | $ / MMBTU		2.12
Commodity Natural Gas Hedges [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair Value Inputs Price Per MMBtu | $ / MMBTU		4.35
Derivative Financial Instruments Liabilities Power Sale Agreements [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)	$ 1
Derivative Financial Instruments Liabilities Power Sale Agreements [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh	18.50
Derivative Financial Instruments Liabilities Power Sale Agreements [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh	84.35
Financial Transmission Rights [Member] | RTO Auction Pricing [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)	$ 16	$ 14
Financial Transmission Rights [Member] | Minimum [Member] | RTO Auction Pricing [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh	(0.81)	(1.92)
Financial Transmission Rights [Member] | Maximum [Member] | RTO Auction Pricing [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh	7.23	9.86
Commodity Power Contracts [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)		$ (1)
Commodity Power Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh		25.16
Commodity Power Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh		51.75
Commodity Capacity Option Contracts [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)		$ 2
Commodity Capacity Option Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair Value Inputs Price Per MW day | $ / MW		21.00
Commodity Capacity Option Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair Value Inputs Price Per MW day | $ / MW		109.00
Derivative Financial Instruments Liabilities Reserves [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)		$ (11)
Duke Energy Ohio [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)		(18)
Duke Energy Ohio [Member] | Commodity Natural Gas Hedges [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)		$ (5)
Duke Energy Ohio [Member] | Commodity Natural Gas Hedges [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair Value Inputs Price Per MMBtu | $ / MMBTU		2.12
Duke Energy Ohio [Member] | Commodity Natural Gas Hedges [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair Value Inputs Price Per MMBtu | $ / MMBTU		4.35
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | RTO Auction Pricing [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)	$ 4
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Minimum [Member] | RTO Auction Pricing [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh	0.37
Duke Energy Ohio [Member] | Financial Transmission Rights [Member] | Maximum [Member] | RTO Auction Pricing [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh	2.17
Duke Energy Ohio [Member] | Commodity Power Contracts [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)		$ (6)
Duke Energy Ohio [Member] | Commodity Power Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh		25.25
Duke Energy Ohio [Member] | Commodity Power Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh		51.75
Duke Energy Ohio [Member] | Derivative Financial Instruments Liabilities Reserves [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)		$ (7)
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | RTO Auction Pricing [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Net derivative asset (liability)	$ 12	$ 14
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Minimum [Member] | RTO Auction Pricing [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh	(0.81)	(1.92)
Duke Energy Indiana [Member] | Financial Transmission Rights [Member] | Maximum [Member] | RTO Auction Pricing [Member]
Net Derivative Asset (Liability) Fair Value Inputs [Line Items]
Fair value inputs, price per MWh | $ / MWh	7.23	9.86