Investments in Debt and Equity Securities (Estimated Fair Value of Investments in Debt and Equity Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale
Estimated Fair Value	$ 3,296
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	4,927	$ 4,387
Unrealized Holding Losses	43	55
Estimated Fair Value	10,441	9,687
Duke Energy Carolinas
Debt Securities, Available-for-sale
Estimated Fair Value	1,468
Progress Energy
Debt Securities, Available-for-sale
Estimated Fair Value	1,571
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2,036	1,769
Unrealized Holding Losses	23	31
Estimated Fair Value	4,493	4,296
Duke Energy Progress
Debt Securities, Available-for-sale
Estimated Fair Value	1,061
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,940	1,687
Unrealized Holding Losses	20	31
Estimated Fair Value	3,865	3,529
Duke Energy Florida
Debt Securities, Available-for-sale
Estimated Fair Value	510
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	96	82
Unrealized Holding Losses	3
Estimated Fair Value	626	663
Duke Energy Indiana
Debt Securities, Available-for-sale
Estimated Fair Value	45
NDTF
Available-for-sale Securities
Cash and cash equivalents	153	177
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	4,710	4,138
Equity Securities, FV-NI, Accumulated Unrealized Loss	31	54
Equity securities, FV-NI	6,743	6,235
Debt Securities, Available-for-sale
Estimated Fair Value	3,012	2,717
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	4,820	4,295
Unrealized Holding Losses	42	55
Estimated Fair Value	9,908	9,129
NDTF | Duke Energy Carolinas
Available-for-sale Securities
Cash and cash equivalents	68	30
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	2,729	2,442
Equity Securities, FV-NI, Accumulated Unrealized Loss	14	23
Equity securities, FV-NI	3,910	3,685
Debt Securities, Available-for-sale
Estimated Fair Value	1,468	1,250
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2,787	2,529
Unrealized Holding Losses	19	24
Estimated Fair Value	5,446	4,965
NDTF | Progress Energy
Available-for-sale Securities
Cash and cash equivalents	85	147
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	1,981	1,696
Equity Securities, FV-NI, Accumulated Unrealized Loss	17	31
Equity securities, FV-NI	2,833	2,550
Debt Securities, Available-for-sale
Estimated Fair Value	1,544	1,467
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2,033	1,766
Unrealized Holding Losses	23	31
Estimated Fair Value	4,462	4,164
NDTF | Duke Energy Progress
Available-for-sale Securities
Cash and cash equivalents	73	76
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	1,888	1,617
Equity Securities, FV-NI, Accumulated Unrealized Loss	17	31
Equity securities, FV-NI	2,730	2,459
Debt Securities, Available-for-sale
Estimated Fair Value	1,061	993
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,940	1,687
Unrealized Holding Losses	20	31
Estimated Fair Value	3,864	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	103	91
Debt Securities, Available-for-sale
Estimated Fair Value	483	474
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	93	79
Unrealized Holding Losses	3
Estimated Fair Value	598	636
Other Investments
Available-for-sale Securities
Cash and cash equivalents	83	127
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	98	79
Equity securities, FV-NI	166	146
Debt Securities, Available-for-sale
Estimated Fair Value	284	285
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	107	92
Unrealized Holding Losses	1
Estimated Fair Value	533	558
Other Investments | Progress Energy
Available-for-sale Securities
Cash and cash equivalents	4	106
Debt Securities, Available-for-sale
Estimated Fair Value	27	26
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	3	3
Estimated Fair Value	31	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	1	1
Debt Securities, Available-for-sale
Estimated Fair Value	27	26
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	3	3
Estimated Fair Value	28	27
Other Investments | Duke Energy Indiana
Available-for-sale Securities
Cash and cash equivalents	1	1
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	70	58
Equity securities, FV-NI	110	97
Debt Securities, Available-for-sale
Estimated Fair Value	45	45
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	71	59
Unrealized Holding Losses	1
Estimated Fair Value	156	143
Corporate debt securities | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	51	76
Gross Unrealized Holding Losses	3	1
Estimated Fair Value	861	806
Corporate debt securities | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	32	49
Gross Unrealized Holding Losses	2	1
Estimated Fair Value	495	510
Corporate debt securities | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	19	27
Gross Unrealized Holding Losses	1
Estimated Fair Value	366	296
Corporate debt securities | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	19	27
Gross Unrealized Holding Losses	1
Estimated Fair Value	299	296
Corporate debt securities | NDTF | Duke Energy Florida
Debt Securities, Available-for-sale
Estimated Fair Value	67
Corporate debt securities | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	4	8
Estimated Fair Value	118	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	17	22
Estimated Fair Value	298	370
Municipal bonds | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	2	6
Estimated Fair Value	21	91
Municipal bonds | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	15	16
Estimated Fair Value	277	279
Municipal bonds | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	15	16
Estimated Fair Value	277	279
Municipal bonds | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	4	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	3	3
Estimated Fair Value	27	26
Municipal bonds | Other Investments | Duke Energy Florida
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	3	3
Estimated Fair Value	27	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	36	51
Gross Unrealized Holding Losses	8
Estimated Fair Value	1,665	1,361
U.S. government bonds | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	19	25
Gross Unrealized Holding Losses	3
Estimated Fair Value	770	475
U.S. government bonds | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	17	26
Gross Unrealized Holding Losses	5
Estimated Fair Value	895	886
U.S. government bonds | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	17	26
Gross Unrealized Holding Losses	2
Estimated Fair Value	479	412
U.S. government bonds | NDTF | Duke Energy Florida
Debt Securities, Available-for-sale
Gross Unrealized Holding Losses	3
Estimated Fair Value	416	474
U.S. government bonds | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	1
Estimated Fair Value	66	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	6	8
Estimated Fair Value	188	180
Other debt securities | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	5	7
Estimated Fair Value	182	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
Estimated Fair Value	$ 31	$ 47