Investments in Debt and Equity Securities (Available-For-Sale Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	$ 2,899	$ 2,156
Gross Unrealized Holding Losses	42	88
Estimated Fair Value	7,451	6,554
NDTF [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	2,837	2,115
Gross Unrealized Holding Losses	40	83
Estimated Fair Value	7,088	6,184
NDTF [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	115	111
NDTF [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	2,805	2,092
Gross Unrealized Holding Losses	27	54
Estimated Fair Value	4,914	4,106
NDTF [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	17	10
Gross Unrealized Holding Losses	2	8
Estimated Fair Value	570	528
NDTF [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	4	3
Gross Unrealized Holding Losses	3	10
Estimated Fair Value	344	331
NDTF [Member] | US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	11	10
Gross Unrealized Holding Losses	7	8
Estimated Fair Value	1,027	984
NDTF [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Losses	1	3
Estimated Fair Value	118	124
Other Classification [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	62	41
Gross Unrealized Holding Losses	2	5
Estimated Fair Value	363	370
Other Classification [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	15	25
Other Classification [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	59	38
Estimated Fair Value	123	104
Other Classification [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	1	1
Gross Unrealized Holding Losses		1
Estimated Fair Value	57	66
Other Classification [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	2	2
Gross Unrealized Holding Losses	1	1
Estimated Fair Value	83	82
Other Classification [Member] | US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Losses		1
Estimated Fair Value	41	51
Other Classification [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Losses	1	2
Estimated Fair Value	44	42
Duke Energy Carolinas [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	1,543	1,165
Gross Unrealized Holding Losses	20	45
Estimated Fair Value	3,758	3,261
Duke Energy Carolinas [Member] | NDTF [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	1,543	1,165
Gross Unrealized Holding Losses	20	44
Estimated Fair Value	3,758	3,258
Duke Energy Carolinas [Member] | NDTF [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	32	18
Duke Energy Carolinas [Member] | NDTF [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	1,531	1,157
Gross Unrealized Holding Losses	12	28
Estimated Fair Value	2,692	2,245
Duke Energy Carolinas [Member] | NDTF [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	9	5
Gross Unrealized Holding Losses	2	6
Estimated Fair Value	359	354
Duke Energy Carolinas [Member] | NDTF [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains		1
Gross Unrealized Holding Losses	1	2
Estimated Fair Value	60	67
Duke Energy Carolinas [Member] | NDTF [Member] | US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	3	2
Gross Unrealized Holding Losses	4	5
Estimated Fair Value	503	458
Duke Energy Carolinas [Member] | NDTF [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Losses	1	3
Estimated Fair Value	112	116
Duke Energy Carolinas [Member] | Other Classification [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Losses		1
Estimated Fair Value		3
Duke Energy Carolinas [Member] | Other Classification [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Losses		1
Estimated Fair Value		3
Progress Energy [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	1,296	952
Gross Unrealized Holding Losses	20	39
Estimated Fair Value	3,389	2,991
Progress Energy [Member] | NDTF [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	1,294	950
Gross Unrealized Holding Losses	20	39
Estimated Fair Value	3,330	2,926
Progress Energy [Member] | NDTF [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	83	93
Progress Energy [Member] | NDTF [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	1,274	935
Gross Unrealized Holding Losses	15	26
Estimated Fair Value	2,222	1,861
Progress Energy [Member] | NDTF [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	8	5
Gross Unrealized Holding Losses		2
Estimated Fair Value	211	174
Progress Energy [Member] | NDTF [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	4	2
Gross Unrealized Holding Losses	2	8
Estimated Fair Value	284	264
Progress Energy [Member] | NDTF [Member] | US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	8	8
Gross Unrealized Holding Losses	3	3
Estimated Fair Value	524	526
Progress Energy [Member] | NDTF [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	6	8
Progress Energy [Member] | Other Classification [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	2	2
Estimated Fair Value	59	65
Progress Energy [Member] | Other Classification [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	12	21
Progress Energy [Member] | Other Classification [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	2	2
Estimated Fair Value	47	44
Duke Energy Progress [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	995	715
Gross Unrealized Holding Losses	16	32
Estimated Fair Value	2,592	2,214
Duke Energy Progress [Member] | NDTF [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	995	715
Gross Unrealized Holding Losses	16	32
Estimated Fair Value	2,591	2,213
Duke Energy Progress [Member] | NDTF [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	50	45
Duke Energy Progress [Member] | NDTF [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	980	704
Gross Unrealized Holding Losses	12	21
Estimated Fair Value	1,795	1,505
Duke Energy Progress [Member] | NDTF [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	6	4
Gross Unrealized Holding Losses		1
Estimated Fair Value	149	120
Duke Energy Progress [Member] | NDTF [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	4	2
Gross Unrealized Holding Losses	2	8
Estimated Fair Value	283	263
Duke Energy Progress [Member] | NDTF [Member] | US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	5	5
Gross Unrealized Holding Losses	2	2
Estimated Fair Value	310	275
Duke Energy Progress [Member] | NDTF [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	4	5
Duke Energy Progress [Member] | Other Classification [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	1	1
Duke Energy Progress [Member] | Other Classification [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	1	1
Duke Energy Florida [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	301	237
Gross Unrealized Holding Losses	4	7
Estimated Fair Value	787	761
Duke Energy Florida [Member] | NDTF [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	299	235
Gross Unrealized Holding Losses	4	7
Estimated Fair Value	739	713
Duke Energy Florida [Member] | NDTF [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	33	48
Duke Energy Florida [Member] | NDTF [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	294	231
Gross Unrealized Holding Losses	3	5
Estimated Fair Value	427	356
Duke Energy Florida [Member] | NDTF [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	2	1
Gross Unrealized Holding Losses		1
Estimated Fair Value	62	54
Duke Energy Florida [Member] | NDTF [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	1	1
Duke Energy Florida [Member] | NDTF [Member] | US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	3	3
Gross Unrealized Holding Losses	1	1
Estimated Fair Value	214	251
Duke Energy Florida [Member] | NDTF [Member] | Other Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	2	3
Duke Energy Florida [Member] | Other Classification [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	2	2
Estimated Fair Value	48	48
Duke Energy Florida [Member] | Other Classification [Member] | Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	1	4
Duke Energy Florida [Member] | Other Classification [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	2	2
Estimated Fair Value	47	44
Duke Energy Indiana [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	49	33
Gross Unrealized Holding Losses	1	1
Estimated Fair Value	128	110
Duke Energy Indiana [Member] | Other Classification [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	49	33
Gross Unrealized Holding Losses	1	1
Estimated Fair Value	128	110
Duke Energy Indiana [Member] | Other Classification [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Gains	49	33
Estimated Fair Value	97	79
Duke Energy Indiana [Member] | Other Classification [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	3	2
Duke Energy Indiana [Member] | Other Classification [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Holding Losses	1	1
Estimated Fair Value	$ 28	28
Duke Energy Indiana [Member] | Other Classification [Member] | US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value		$ 1