Investments in Debt and Equity Securities (Estimated Fair Value of Investments in Debt and Equity Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale
Estimated Fair Value	$ 2,532
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	3,662	$ 3,675
Unrealized Holding Losses	106	57
Estimated Fair Value	8,914	8,562
Duke Energy Carolinas
Debt Securities, Available-for-sale
Estimated Fair Value	1,232
Progress Energy
Debt Securities, Available-for-sale
Estimated Fair Value	1,045
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,482	1,655
Unrealized Holding Losses	52	47
Estimated Fair Value	4,027	3,883
Duke Energy Progress
Debt Securities, Available-for-sale
Estimated Fair Value	992
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,409	1,300
Unrealized Holding Losses	52	21
Estimated Fair Value	3,200	3,053
Duke Energy Florida
Debt Securities, Available-for-sale
Estimated Fair Value	53
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	73	355
Unrealized Holding Losses		26
Estimated Fair Value	723	787
Duke Energy Indiana
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	45	43
Equity securities, FV-NI	84	81
Debt Securities, Available-for-sale
Estimated Fair Value	45
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	46	44
Unrealized Holding Losses	1
Estimated Fair Value	130	125
NDTF
Available-for-sale Securities
Cash and cash equivalents	687	101
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	3,436	3,523
Equity Securities, FV-NI, Accumulated Unrealized Loss	103	55
Equity securities, FV-NI	5,459	5,661
Debt Securities, Available-for-sale
Estimated Fair Value	2,224	2,368
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	3,587	3,609
Unrealized Holding Losses	105	57
Estimated Fair Value	8,370	8,130
NDTF | Duke Energy Carolinas
Available-for-sale Securities
Cash and cash equivalents	42	21
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	2,027	1,914
Equity Securities, FV-NI, Accumulated Unrealized Loss	52	8
Equity securities, FV-NI	3,229	3,154
Debt Securities, Available-for-sale
Estimated Fair Value	1,232	1,172
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	2,109	1,957
Unrealized Holding Losses	53	10
Estimated Fair Value	4,503	4,347
NDTF | Progress Energy
Available-for-sale Securities
Cash and cash equivalents	645	80
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	1,409	1,609
Equity Securities, FV-NI, Accumulated Unrealized Loss	51	47
Equity securities, FV-NI	2,230	2,507
Debt Securities, Available-for-sale
Estimated Fair Value	992	1,196
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,478	1,652
Unrealized Holding Losses	52	47
Estimated Fair Value	3,867	3,783
NDTF | Duke Energy Progress
Available-for-sale Securities
Cash and cash equivalents	57	53
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	1,340	1,258
Equity Securities, FV-NI, Accumulated Unrealized Loss	51	21
Equity securities, FV-NI	2,150	2,077
Debt Securities, Available-for-sale
Estimated Fair Value	992	921
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	1,409	1,300
Unrealized Holding Losses	52	21
Estimated Fair Value	3,199	3,051
NDTF | Duke Energy Florida
Available-for-sale Securities
Cash and cash equivalents	588	27
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	69	351
Equity Securities, FV-NI, Accumulated Unrealized Loss		26
Equity securities, FV-NI	80	430
Debt Securities, Available-for-sale
Estimated Fair Value		275
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	69	352
Unrealized Holding Losses		26
Estimated Fair Value	668	732
Other Investments
Available-for-sale Securities
Cash and cash equivalents	110	52
Equity Securities, FV-NI
Equity Securities, FV-NI, Accumulated Unrealized Gain	60	57
Equity securities, FV-NI	126	122
Debt Securities, Available-for-sale
Estimated Fair Value	308	258
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	75	66
Unrealized Holding Losses	1
Estimated Fair Value	544	432
Other Investments | Progress Energy
Available-for-sale Securities
Cash and cash equivalents	107	49
Debt Securities, Available-for-sale
Estimated Fair Value	53	51
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	4	3
Estimated Fair Value	160	100
Other Investments | Duke Energy Progress
Available-for-sale Securities
Cash and cash equivalents	1	2
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Estimated Fair Value	1	2
Other Investments | Duke Energy Florida
Available-for-sale Securities
Cash and cash equivalents	2	4
Debt Securities, Available-for-sale
Estimated Fair Value	53	51
Investments, Accumulated Gross Unrealized Gains (Losses) [Abstract]
Unrealized Holding Gains	4	3
Estimated Fair Value	55	55
Other Investments | Duke Energy Indiana
Available-for-sale Securities
Cash and cash equivalents	1
Equity Securities, FV-NI
Equity securities, FV-NI	84	81
Debt Securities, Available-for-sale
Estimated Fair Value	45	44
Corporate debt securities | Duke Energy Indiana
Debt Securities, Available-for-sale
Estimated Fair Value	3	6
Corporate debt securities | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	65	37
Gross Unrealized Holding Losses	1	1
Estimated Fair Value	789	603
Corporate debt securities | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	42	21
Gross Unrealized Holding Losses	1	1
Estimated Fair Value	507	361
Corporate debt securities | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	23	16
Estimated Fair Value	282	242
Corporate debt securities | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	23	16
Estimated Fair Value	282	242
Corporate debt securities | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	8	3
Estimated Fair Value	129	67
Municipal bonds | Duke Energy Indiana
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	1	1
Gross Unrealized Holding Losses	1
Estimated Fair Value	39	36
Municipal bonds | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	19	13
Gross Unrealized Holding Losses	1
Estimated Fair Value	407	368
Municipal bonds | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	5	3
Estimated Fair Value	118	96
Municipal bonds | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	14	10
Gross Unrealized Holding Losses	1
Estimated Fair Value	289	272
Municipal bonds | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	14	10
Gross Unrealized Holding Losses	1
Estimated Fair Value	289	272
Municipal bonds | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	6	4
Gross Unrealized Holding Losses	1
Estimated Fair Value	114	94
Municipal bonds | Other Investments | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	4	3
Estimated Fair Value	53	51
Municipal bonds | Other Investments | Duke Energy Florida
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	4	3
Estimated Fair Value	53	51
U.S. government bonds | Duke Energy Indiana
Debt Securities, Available-for-sale
Estimated Fair Value	3	2
U.S. government bonds | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	58	33
Gross Unrealized Holding Losses		1
Estimated Fair Value	843	1,256
U.S. government bonds | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	28	16
Gross Unrealized Holding Losses		1
Estimated Fair Value	428	578
U.S. government bonds | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	30	17
Estimated Fair Value	415	678
U.S. government bonds | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	30	16
Estimated Fair Value	415	403
U.S. government bonds | NDTF | Duke Energy Florida
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains		1
Estimated Fair Value		275
U.S. government bonds | Other Investments
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	1	2
Estimated Fair Value	21	41
Other debt securities | NDTF
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	9	3
Estimated Fair Value	185	141
Other debt securities | NDTF | Duke Energy Carolinas
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	7	3
Estimated Fair Value	179	137
Other debt securities | NDTF | Progress Energy
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	2
Estimated Fair Value	6	4
Other debt securities | NDTF | Duke Energy Progress
Debt Securities, Available-for-sale
Gross Unrealized Holding Gains	2
Estimated Fair Value	6	4
Other debt securities | Other Investments
Debt Securities, Available-for-sale
Estimated Fair Value	$ 44	$ 56