Investments in Debt and Equity Securities (Estimated Fair Value of Investments in Debt and Equity Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale
Estimated Fair Value	$ 3,112
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	4,541	$ 4,387
Unrealized Holding Losses	77	55
Estimated Fair Value	10,060	9,687
Duke Energy Carolinas
Debt Securities, Available-for-sale
Estimated Fair Value	1,344
Progress Energy
Debt Securities, Available-for-sale
Estimated Fair Value	1,517
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,878	1,769
Unrealized Holding Losses	37	31
Estimated Fair Value	4,395	4,296
Duke Energy Progress
Debt Securities, Available-for-sale
Estimated Fair Value	1,003
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,790	1,687
Unrealized Holding Losses	32	31
Estimated Fair Value	3,646	3,529
Duke Energy Florida
Debt Securities, Available-for-sale
Estimated Fair Value	514
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	88	82
Unrealized Holding Losses	5
Estimated Fair Value	645	663
Duke Energy Indiana
Debt Securities, Available-for-sale
Estimated Fair Value	45
NDTF
Available-for-sale Securities
Cash and cash equivalents	193	177
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	4,363	4,138
Equity Securities, FV-NI, Accumulated Unrealized Loss	47	54
Equity securities, FV-NI	6,379	6,235
Debt Securities, Available-for-sale
Estimated Fair Value	2,835	2,717
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	4,450	4,295
Unrealized Holding Losses	74	55
Estimated Fair Value	9,407	9,129
NDTF | Duke Energy Carolinas
Available-for-sale Securities
Cash and cash equivalents	63	30
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	2,531	2,442
Equity Securities, FV-NI, Accumulated Unrealized Loss	23	23
Equity securities, FV-NI	3,738	3,685
Debt Securities, Available-for-sale
Estimated Fair Value	1,344	1,250
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2,574	2,529
Unrealized Holding Losses	37	24
Estimated Fair Value	5,145	4,965
NDTF | Progress Energy
Available-for-sale Securities
Cash and cash equivalents	130	147
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	1,832	1,696
Equity Securities, FV-NI, Accumulated Unrealized Loss	24	31
Equity securities, FV-NI	2,641	2,550
Debt Securities, Available-for-sale
Estimated Fair Value	1,491	1,467
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,876	1,766
Unrealized Holding Losses	37	31
Estimated Fair Value	4,262	4,164
NDTF | Duke Energy Progress
Available-for-sale Securities
Cash and cash equivalents	95	76
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	1,746	1,617
Equity Securities, FV-NI, Accumulated Unrealized Loss	24	31
Equity securities, FV-NI	2,547	2,459
Debt Securities, Available-for-sale
Estimated Fair Value	1,003	993
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,790	1,687
Unrealized Holding Losses	32	31
Estimated Fair Value	3,645	3,528
NDTF | Duke Energy Florida
Available-for-sale Securities
Cash and cash equivalents	35	71
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	86	79
Equity securities, FV-NI	94	91
Debt Securities, Available-for-sale
Estimated Fair Value	488	474
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	86	79
Unrealized Holding Losses	5
Estimated Fair Value	617	636
Other Investments
Available-for-sale Securities
Cash and cash equivalents	222	127
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	86	79
Equity securities, FV-NI	154	146
Debt Securities, Available-for-sale
Estimated Fair Value	277	285
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	91	92
Unrealized Holding Losses	3
Estimated Fair Value	653	558
Other Investments | Progress Energy
Available-for-sale Securities
Cash and cash equivalents	107	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	133	132
Other Investments | Duke Energy Progress
Available-for-sale Securities
Cash and cash equivalents	1	1
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Estimated Fair Value	1	1
Other Investments | Duke Energy Florida
Available-for-sale Securities
Cash and cash equivalents	2	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	28	27
Other Investments | Duke Energy Indiana
Available-for-sale Securities
Cash and cash equivalents		1
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	62	58
Equity securities, FV-NI	102	97
Debt Securities, Available-for-sale
Estimated Fair Value	45	45
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	63	59
Unrealized Holding Losses	1
Estimated Fair Value	147	143
Corporate debt securities | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	38	76
Gross Unrealized Holding Losses	8	1
Estimated Fair Value	793	806
Corporate debt securities | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	23	49
Gross Unrealized Holding Losses	5	1
Estimated Fair Value	475	510
Corporate debt securities | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	15	27
Gross Unrealized Holding Losses	3
Estimated Fair Value	318	296
Corporate debt securities | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	15	27
Gross Unrealized Holding Losses	3
Estimated Fair Value	291	296
Corporate debt securities | NDTF | Duke Energy Florida
Debt Securities, Available-for-sale
Estimated Fair Value	27
Corporate debt securities | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	2	8
Estimated Fair Value	109	110
Corporate debt securities | Other Investments | Duke Energy Indiana
Debt Securities, Available-for-sale
Estimated Fair Value	4	3
Municipal bonds | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	13	22
Gross Unrealized Holding Losses	1
Estimated Fair Value	299	370
Municipal bonds | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains		6
Estimated Fair Value	22	91
Municipal bonds | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	13	16
Gross Unrealized Holding Losses	1
Estimated Fair Value	277	279
Municipal bonds | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	13	16
Gross Unrealized Holding Losses	1
Estimated Fair Value	277	279
Municipal bonds | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	3	5
Gross Unrealized Holding Losses	1
Estimated Fair Value	77	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	35	38
U.S. government bonds | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	31	51
Gross Unrealized Holding Losses	18
Estimated Fair Value	1,559	1,361
U.S. government bonds | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	16	25
Gross Unrealized Holding Losses	9
Estimated Fair Value	669	475
U.S. government bonds | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	15	26
Gross Unrealized Holding Losses	9
Estimated Fair Value	890	886
U.S. government bonds | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	15	26
Gross Unrealized Holding Losses	4
Estimated Fair Value	429	412
U.S. government bonds | NDTF | Duke Energy Florida
Debt Securities, Available-for-sale
Gross Unrealized Holding Losses	5
Estimated Fair Value	461	474
U.S. government bonds | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Losses	1
Estimated Fair Value	55	42
U.S. government bonds | Other Investments | Duke Energy Indiana
Debt Securities, Available-for-sale
Estimated Fair Value	6	4
Other debt securities | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	5	8
Estimated Fair Value	184	180
Other debt securities | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	4	7
Estimated Fair Value	178	174
Other debt securities | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	1	1
Estimated Fair Value	6	6
Other debt securities | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	1	1
Estimated Fair Value	6	6
Other debt securities | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Losses	1
Estimated Fair Value	$ 36	$ 47