Fair Value Measurements (Reconciliation of Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs) (Details) - USD ($)	2 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2016	Dec. 31, 2015	Oct. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurement Transfers Between Activity Levels		$ 0	$ 0		$ 0
Investments
Beginning balance		5,000,000	5,000,000
Total pretax realized and unrealized gains included in comprehensive income		1,000,000
Sales		(6,000,000)
Ending balance	$ 5,000,000		5,000,000		5,000,000
Derivatives (net)
Beginning balance		(166,000,000)	10,000,000
Derivative Liability Resulting From Piedmont Acquisition			(187,000,000)
Purchases		55,000,000	33,000,000
Settlements		(47,000,000)	(28,000,000)
Total gains (losses) included on the Consolidated Balance Sheet		44,000,000	6,000,000
Ending balance	(166,000,000)	(114,000,000)	(166,000,000)		10,000,000
Investments and Derivatives, Net
Beginning balance		(161,000,000)	15,000,000
Total pretax realized or unrealized gains included in other comprehensive income		1,000,000
Derivative Liability Resulting From Piedmont Acquisition			(187,000,000)
Purchases		55,000,000	33,000,000
Sales		(6,000,000)
Settlements		(47,000,000)	(28,000,000)
Total gains (losses) included on the Consolidated Balance Sheet		44,000,000	6,000,000
Ending balance	(161,000,000)	(114,000,000)	(161,000,000)		15,000,000
Duke Energy Carolinas [Member]
Investments
Beginning balance		3,000,000	3,000,000
Total pretax realized and unrealized gains included in comprehensive income		1,000,000
Sales		(4,000,000)
Ending balance	3,000,000		3,000,000		3,000,000
Duke Energy Ohio [Member]
Derivatives (net)
Beginning balance		5,000,000	3,000,000
Purchases		3,000,000	5,000,000
Settlements		(4,000,000)	(5,000,000)
Total gains (losses) included on the Consolidated Balance Sheet		(3,000,000)	2,000,000
Ending balance	5,000,000	1,000,000	5,000,000		3,000,000
Duke Energy Indiana [Member]
Derivatives (net)
Beginning balance		16,000,000	7,000,000
Purchases		52,000,000	29,000,000
Settlements		(43,000,000)	(24,000,000)
Total gains (losses) included on the Consolidated Balance Sheet		2,000,000	4,000,000
Ending balance	16,000,000	27,000,000	16,000,000		$ 7,000,000
Piedmont Natural Gas [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurement Transfers Between Activity Levels	0			$ 0		$ 0
Derivatives (net)
Beginning balance	(188,000,000)	(187,000,000)
Total gains (losses) and settlements	1,000,000	45,000,000		(188,000,000)
Ending balance	$ (187,000,000)	$ (142,000,000)	$ (187,000,000)	$ (188,000,000)