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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
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	(115,000,000)	(124,000,000)	(113,000,000)	(114,000,000)
Purchases, sales, issuances and settlements:
Purchases	38,000,000	56,000,000	38,000,000	56,000,000
Settlements	(11,000,000)	15,000,000	(23,000,000)	(29,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	9,000,000	(14,000,000)	19,000,000	(10,000,000)
Balance at end of period	(79,000,000)	(97,000,000)	(79,000,000)	(97,000,000)
Duke Energy Indiana [Member]
Derivatives (net)
Balance at beginning of period	5,000,000		22,000,000	27,000,000
Purchases, sales, issuances and settlements:
Purchases	29,000,000	49,000,000	29,000,000	49,000,000
Settlements	(9,000,000)	(14,000,000)	(19,000,000)	(28,000,000)
Total gains (losses) included on the Condensed Consolidated Balance Sheet	3,000,000	2,000,000	(4,000,000)	(4,000,000)
Balance at end of period	28,000,000	44,000,000	28,000,000	44,000,000
Piedmont Natural Gas [Member]
Derivatives (net)
Balance at beginning of period	(121,000,000)	(132,000,000)	(141,000,000)	(142,000,000)
Purchases, sales, issuances and settlements:
Total gains (losses) and settlements	7,000,000	(18,000,000)	27,000,000	(8,000,000)
Balance at end of period	$ (114,000,000)	$ (150,000,000)	$ (114,000,000)	$ (150,000,000)