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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
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	(124,000,000)	(135,000,000)	(114,000,000)	(166,000,000)
Purchases	56,000,000	55,000,000	56,000,000	55,000,000
Settlements	(15,000,000)	(9,000,000)	(29,000,000)	(18,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	(14,000,000)	(2,000,000)	(10,000,000)	38,000,000
Ending balance	(97,000,000)	(91,000,000)	(97,000,000)	(91,000,000)
Investments and Derivatives, Net
Beginning balance	(124,000,000)	(130,000,000)	(114,000,000)	(161,000,000)
Total pretax realized or unrealized gains included in comprehensive income		1,000,000		1,000,000
Purchases	56,000,000	55,000,000	56,000,000	55,000,000
Sales		(6,000,000)		(6,000,000)
Settlements	(15,000,000)	(9,000,000)	(29,000,000)	(18,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	(14,000,000)	(2,000,000)	(10,000,000)	38,000,000
Ending balance	(97,000,000)	(91,000,000)	(97,000,000)	(91,000,000)
Investments [Member]
Investments
Beginning balance		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)
Duke Energy Carolinas [Member] | Investments [Member]
Investments
Beginning balance		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)
Duke Energy Ohio [Member]
Derivatives (net)
Beginning balance	1,000,000	1,000,000	1,000,000	5,000,000
Purchases	7,000,000	3,000,000	7,000,000	3,000,000
Settlements	(1,000,000)	(1,000,000)	(1,000,000)	(2,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	2,000,000		2,000,000	(3,000,000)
Ending balance	9,000,000	3,000,000	9,000,000	3,000,000
Duke Energy Indiana [Member]
Derivatives (net)
Beginning balance	7,000,000	9,000,000	27,000,000	16,000,000
Purchases	49,000,000	52,000,000	49,000,000	52,000,000
Settlements	(14,000,000)	(9,000,000)	(28,000,000)	(16,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	2,000,000	(1,000,000)	(4,000,000)	(1,000,000)
Ending balance	44,000,000	51,000,000	44,000,000	51,000,000
Piedmont Natural Gas [Member]
Derivatives (net)
Beginning balance	(132,000,000)	(145,000,000)	(142,000,000)	(187,000,000)
Total gains (losses) and settlements	(18,000,000)		(8,000,000)	42,000,000
Ending balance	$ (150,000,000)	$ (145,000,000)	$ (150,000,000)	$ (145,000,000)