Investments in Debt and Equity Securities (Estimated Fair Value of Investments in Debt and Equity Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale
Estimated Fair Value	$ 3,226
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	4,885	$ 4,387
Unrealized Holding Losses	52	55
Estimated Fair Value	10,376	9,687
Duke Energy Carolinas
Debt Securities, Available-for-sale
Estimated Fair Value	1,461
Progress Energy
Debt Securities, Available-for-sale
Estimated Fair Value	1,508
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2,022	1,769
Unrealized Holding Losses	30	31
Estimated Fair Value	4,472	4,296
Duke Energy Progress
Debt Securities, Available-for-sale
Estimated Fair Value	1,030
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,927	1,687
Unrealized Holding Losses	26	31
Estimated Fair Value	3,874	3,529
Duke Energy Florida
Debt Securities, Available-for-sale
Estimated Fair Value	478
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	95	82
Unrealized Holding Losses	4
Estimated Fair Value	597	663
Duke Energy Indiana
Debt Securities, Available-for-sale
Estimated Fair Value	46
NDTF
Available-for-sale Securities
Cash and cash equivalents	164	177
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	4,700	4,138
Equity Securities, FV-NI, Accumulated Unrealized Loss	35	54
Equity securities, FV-NI	6,754	6,235
Debt Securities, Available-for-sale
Estimated Fair Value	2,943	2,717
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	4,795	4,295
Unrealized Holding Losses	50	55
Estimated Fair Value	9,861	9,129
NDTF | Duke Energy Carolinas
Available-for-sale Securities
Cash and cash equivalents	60	30
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	2,725	2,442
Equity Securities, FV-NI, Accumulated Unrealized Loss	14	23
Equity securities, FV-NI	3,912	3,685
Debt Securities, Available-for-sale
Estimated Fair Value	1,461	1,250
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2,775	2,529
Unrealized Holding Losses	20	24
Estimated Fair Value	5,433	4,965
NDTF | Progress Energy
Available-for-sale Securities
Cash and cash equivalents	104	147
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	1,975	1,696
Equity Securities, FV-NI, Accumulated Unrealized Loss	21	31
Equity securities, FV-NI	2,842	2,550
Debt Securities, Available-for-sale
Estimated Fair Value	1,482	1,467
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2,020	1,766
Unrealized Holding Losses	30	31
Estimated Fair Value	4,428	4,164
NDTF | Duke Energy Progress
Available-for-sale Securities
Cash and cash equivalents	92	76
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	1,882	1,617
Equity Securities, FV-NI, Accumulated Unrealized Loss	21	31
Equity securities, FV-NI	2,736	2,459
Debt Securities, Available-for-sale
Estimated Fair Value	1,030	993
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,927	1,687
Unrealized Holding Losses	26	31
Estimated Fair Value	3,858	3,528
NDTF | Duke Energy Florida
Available-for-sale Securities
Cash and cash equivalents	12	71
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	93	79
Equity securities, FV-NI	106	91
Debt Securities, Available-for-sale
Estimated Fair Value	452	474
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	93	79
Unrealized Holding Losses	4
Estimated Fair Value	570	636
Other Investments
Available-for-sale Securities
Cash and cash equivalents	87	127
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	83	79
Equity securities, FV-NI	145	146
Debt Securities, Available-for-sale
Estimated Fair Value	283	285
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	90	92
Unrealized Holding Losses	2
Estimated Fair Value	515	558
Other Investments | Progress Energy
Available-for-sale Securities
Cash and cash equivalents	18	106
Debt Securities, Available-for-sale
Estimated Fair Value	26	26
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2	3
Estimated Fair Value	44	132
Other Investments | Duke Energy Progress
Available-for-sale Securities
Cash and cash equivalents	16	1
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Estimated Fair Value	16	1
Other Investments | Duke Energy Florida
Available-for-sale Securities
Cash and cash equivalents	1	1
Debt Securities, Available-for-sale
Estimated Fair Value	26	26
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2	3
Estimated Fair Value	27	27
Other Investments | Duke Energy Indiana
Available-for-sale Securities
Cash and cash equivalents	19	1
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	56	58
Equity securities, FV-NI	90	97
Debt Securities, Available-for-sale
Estimated Fair Value	46	45
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	57	59
Unrealized Holding Losses	1
Estimated Fair Value	155	143
Corporate debt securities | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	44	76
Gross Unrealized Holding Losses	5	1
Estimated Fair Value	847	806
Corporate debt securities | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	27	49
Gross Unrealized Holding Losses	3	1
Estimated Fair Value	495	510
Corporate debt securities | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	17	27
Gross Unrealized Holding Losses	2
Estimated Fair Value	352	296
Corporate debt securities | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	17	27
Gross Unrealized Holding Losses	2
Estimated Fair Value	287	296
Corporate debt securities | NDTF | Duke Energy Florida
Debt Securities, Available-for-sale
Estimated Fair Value	65
Corporate debt securities | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	4	8
Gross Unrealized Holding Losses	1
Estimated Fair Value	130	110
Corporate debt securities | Other Investments | Duke Energy Indiana
Debt Securities, Available-for-sale
Estimated Fair Value	5	3
Municipal bonds | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	13	22
Gross Unrealized Holding Losses	1
Estimated Fair Value	296	370
Municipal bonds | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	1	6
Estimated Fair Value	24	91
Municipal bonds | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	12	16
Gross Unrealized Holding Losses	1
Estimated Fair Value	272	279
Municipal bonds | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	12	16
Gross Unrealized Holding Losses	1
Estimated Fair Value	272	279
Municipal bonds | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	3	5
Gross Unrealized Holding Losses	1
Estimated Fair Value	69	86
Municipal bonds | Other Investments | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	2	3
Estimated Fair Value	26	26
Municipal bonds | Other Investments | Duke Energy Florida
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	2	3
Estimated Fair Value	26	26
Municipal bonds | Other Investments | Duke Energy Indiana
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	1	1
Gross Unrealized Holding Losses	1
Estimated Fair Value	36	38
U.S. government bonds | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	34	51
Gross Unrealized Holding Losses	8
Estimated Fair Value	1,605	1,361
U.S. government bonds | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	18	25
Gross Unrealized Holding Losses	2
Estimated Fair Value	752	475
U.S. government bonds | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	16	26
Gross Unrealized Holding Losses	6
Estimated Fair Value	853	886
U.S. government bonds | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	16	26
Gross Unrealized Holding Losses	2
Estimated Fair Value	466	412
U.S. government bonds | NDTF | Duke Energy Florida
Debt Securities, Available-for-sale
Gross Unrealized Holding Losses	4
Estimated Fair Value	387	474
U.S. government bonds | Other Investments
Debt Securities, Available-for-sale
Estimated Fair Value	50	42
U.S. government bonds | Other Investments | Duke Energy Indiana
Debt Securities, Available-for-sale
Estimated Fair Value	5	4
Other debt securities | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	4	8
Gross Unrealized Holding Losses	1
Estimated Fair Value	195	180
Other debt securities | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	4	7
Gross Unrealized Holding Losses	1
Estimated Fair Value	190	174
Other debt securities | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains		1
Estimated Fair Value	5	6
Other debt securities | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains		1
Estimated Fair Value	5	6
Other debt securities | Other Investments
Debt Securities, Available-for-sale
Estimated Fair Value	$ 34	$ 47