Fair Value Measurements (Reconciliation of Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurement Transfers Between Activity Levels	$ 0	$ 0	$ 0	$ 0
Derivatives (net)
Beginning balance	(135,000,000)	2,000,000	(166,000,000)	10,000,000
Purchases	55,000,000	34,000,000	55,000,000	34,000,000
Settlements	(9,000,000)	(6,000,000)	(18,000,000)	(13,000,000)
Total (losses) gains included on the Condensed Consolidated Balance Sheet	(2,000,000)	4,000,000	38,000,000	3,000,000
Ending balance	(91,000,000)	34,000,000	(91,000,000)	34,000,000
Investments and Derivatives, Net
Beginning balance	(130,000,000)	6,000,000	(161,000,000)	15,000,000
Total pretax realized or unrealized gains included in comprehensive income	1,000,000		1,000,000
Purchases	55,000,000	34,000,000	55,000,000	34,000,000
Sales	(6,000,000)		(6,000,000)	(1,000,000)
Settlements	(9,000,000)	(6,000,000)	(18,000,000)	(13,000,000)
Total amount included on the Condensed Consolidated Balance Sheet as regulatory assets or liabilities	(2,000,000)	4,000,000	38,000,000	3,000,000
Ending balance	(91,000,000)	38,000,000	(91,000,000)	38,000,000
Investments [Member]
Investments
Beginning balance	5,000,000	4,000,000	5,000,000	5,000,000
Total pretax realized or unrealized gains included in comprehensive income	1,000,000		1,000,000
Sales	(6,000,000)		(6,000,000)	(1,000,000)
Ending balance		4,000,000		4,000,000
Duke Energy Carolinas [Member] | Investments [Member]
Investments
Beginning balance	3,000,000	3,000,000	3,000,000	3,000,000
Total pretax realized or unrealized gains included in comprehensive income	1,000,000		1,000,000
Sales	(4,000,000)		(4,000,000)
Ending balance		3,000,000		3,000,000
Duke Energy Ohio [Member]
Derivatives (net)
Beginning balance	1,000,000		5,000,000	3,000,000
Purchases	3,000,000	5,000,000	3,000,000	5,000,000
Settlements	(1,000,000)		(2,000,000)	(2,000,000)
Total (losses) gains included on the Condensed Consolidated Balance Sheet			(3,000,000)	(1,000,000)
Ending balance	3,000,000	5,000,000	3,000,000	5,000,000
Duke Energy Indiana [Member]
Derivatives (net)
Beginning balance	9,000,000	2,000,000	16,000,000	7,000,000
Purchases	52,000,000	29,000,000	52,000,000	29,000,000
Settlements	(9,000,000)	(6,000,000)	(16,000,000)	(11,000,000)
Total (losses) gains included on the Condensed Consolidated Balance Sheet	(1,000,000)	4,000,000	(1,000,000)	4,000,000
Ending balance	51,000,000	29,000,000	51,000,000	29,000,000
Piedmont Natural Gas [Member]
Derivatives (net)
Beginning balance	(145,000,000)	(126,000,000)	(187,000,000)	(149,000,000)
Total gains and settlements		(64,000,000)	42,000,000	(41,000,000)
Ending balance	$ (145,000,000)	$ (190,000,000)	$ (145,000,000)	$ (190,000,000)