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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 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)
Balance at beginning of period	(97,000,000)	(91,000,000)	(114,000,000)	(166,000,000)
Purchases, sales, issuances and settlements:
Purchases			56,000,000	55,000,000
Settlements	(14,000,000)	(12,000,000)	(43,000,000)	(30,000,000)
Total (losses) gains included on the Condensed Consolidated Balance Sheet	(5,000,000)	10,000,000	(15,000,000)	48,000,000
Balance at end of period	(116,000,000)	(93,000,000)	(116,000,000)	(93,000,000)
Investments and Derivatives, Net
Balance at beginning of period	(97,000,000)	(91,000,000)	(114,000,000)	(161,000,000)
Total pretax realized or unrealized gains included in comprehensive income				1,000,000
Purchases, sales, issuances and settlements:
Purchases			56,000,000	55,000,000
Sales				(6,000,000)
Settlements	(14,000,000)	(12,000,000)	(43,000,000)	(30,000,000)
Total (losses) gains included on the Condensed Consolidated Balance Sheet	(5,000,000)	10,000,000	(15,000,000)	48,000,000
Balance at end of period	(116,000,000)	(93,000,000)	(116,000,000)	(93,000,000)
Investments [Member]
Investments
Balance at beginning of period		0		5,000,000
Total pretax realized or unrealized gains included in comprehensive income				1,000,000
Purchases, sales, issuances and settlements:
Sales				(6,000,000)
Duke Energy Carolinas [Member] | Investments [Member]
Investments
Balance at beginning of period				3,000,000
Total pretax realized or unrealized gains included in comprehensive income				1,000,000
Purchases, sales, issuances and settlements:
Sales				(4,000,000)
Duke Energy Ohio [Member]
Derivatives (net)
Balance at beginning of period	9,000,000	3,000,000	1,000,000	5,000,000
Purchases, sales, issuances and settlements:
Purchases	0		7,000,000	3,000,000
Settlements	(1,000,000)	(1,000,000)	(2,000,000)	(3,000,000)
Total (losses) gains included on the Condensed Consolidated Balance Sheet			2,000,000	(3,000,000)
Balance at end of period	8,000,000	2,000,000	8,000,000	2,000,000
Duke Energy Indiana [Member]
Derivatives (net)
Balance at beginning of period	44,000,000	51,000,000	27,000,000	16,000,000
Purchases, sales, issuances and settlements:
Purchases	0	0	49,000,000	52,000,000
Settlements	(13,000,000)	(11,000,000)	(41,000,000)	(27,000,000)
Total (losses) gains included on the Condensed Consolidated Balance Sheet	(2,000,000)	(12,000,000)	(6,000,000)	(13,000,000)
Balance at end of period	29,000,000	28,000,000	29,000,000	28,000,000
Piedmont Natural Gas [Member]
Derivatives (net)
Balance at beginning of period	(150,000,000)	(145,000,000)	(142,000,000)	(187,000,000)
Purchases, sales, issuances and settlements:
Total gains (losses) and settlements	(3,000,000)	22,000,000	(11,000,000)	64,000,000
Balance at end of period	$ (153,000,000)	$ (123,000,000)	$ (153,000,000)	$ (123,000,000)