Fair Value Measurements (Reconciliation of Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 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	(91,000,000)	34,000,000	(166,000,000)	10,000,000
Purchases			55,000,000	34,000,000
Settlements	(12,000,000)	(9,000,000)	(30,000,000)	(22,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	10,000,000	(2,000,000)	48,000,000	1,000,000
Ending balance	(93,000,000)	23,000,000	(93,000,000)	23,000,000
Investments and Derivatives, Net
Beginning balance	(91,000,000)	38,000,000	(161,000,000)	15,000,000
Total pretax realized or unrealized gains included in comprehensive income			1,000,000
Purchases			55,000,000	34,000,000
Sales			(6,000,000)	(1,000,000)
Settlements	(12,000,000)	(9,000,000)	(30,000,000)	(22,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	10,000,000	(2,000,000)	48,000,000	1,000,000
Ending balance	(93,000,000)	27,000,000	(93,000,000)	27,000,000
Investments [Member]
Investments
Beginning balance		4,000,000	5,000,000	5,000,000
Total pretax realized or unrealized gains included in comprehensive income			1,000,000
Sales			(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
Total pretax realized or unrealized gains included in comprehensive income			1,000,000
Sales			(4,000,000)
Ending balance		3,000,000		3,000,000
Duke Energy Ohio [Member]
Derivatives (net)
Beginning balance	3,000,000	5,000,000	5,000,000	3,000,000
Purchases			3,000,000	5,000,000
Settlements	(1,000,000)	(2,000,000)	(3,000,000)	(4,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet			(3,000,000)	(1,000,000)
Ending balance	2,000,000	3,000,000	2,000,000	3,000,000
Duke Energy Indiana [Member]
Derivatives (net)
Beginning balance	51,000,000	29,000,000	16,000,000	7,000,000
Purchases			52,000,000	29,000,000
Settlements	(11,000,000)	(7,000,000)	(27,000,000)	(18,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	(12,000,000)	(2,000,000)	(13,000,000)	2,000,000
Ending balance	28,000,000	20,000,000	28,000,000	20,000,000
Piedmont Natural Gas [Member]
Derivatives (net)
Beginning balance	(145,000,000)	(190,000,000)	(187,000,000)	(149,000,000)
Total gains (losses) and settlements	22,000,000	(5,000,000)	64,000,000	(46,000,000)
Ending balance	$ (123,000,000)	$ (195,000,000)	$ (123,000,000)	$ (195,000,000)