Investments in Debt and Equity Securities (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Available-for-sale Securities [Line Items]

Available-For-Sale Investments

The following table presents the estimated fair value of investments in AFS securities.

	December 31, 2017						December 31, 2016
	Gross		Gross				Gross		Gross
	Unrealized		Unrealized				Unrealized		Unrealized
	Holding		Holding		Estimated		Holding		Holding		Estimated
(in millions)	Gains		Losses		Fair Value		Gains		Losses(a)		Fair Value
NDTF
Cash and cash equivalents	$	—	$	—	$	115	$	—	$	—	$	111
Equity securities	2,805		27		4,914		2,092		54		4,106
Corporate debt securities	17		2		570		10		8		528
Municipal bonds	4		3		344		3		10		331
U.S. government bonds	11		7		1,027		10		8		984
Other debt securities	—		1		118		—		3		124
Total NDTF	$	2,837	$	40	$	7,088	$	2,115	$	83	$	6,184
Other Investments
Cash and cash equivalents	$	—	$	—	$	15	$	—	$	—	$	25
Equity securities	59		—		123		38		—		104
Corporate debt securities	1		—		57		1		1		66
Municipal bonds	2		1		83		2		1		82
U.S. government bonds	—		—		41		—		1		51
Other debt securities	—		1		44		—		2		42
Total Other Investments	$	62	$	2	$	363	$	41	$	5	$	370
Total Investments	$	2,899	$	42	$	7,451	$	2,156	$	88	$	6,554

Investments Classified by Contractual Maturity Date

The table below summarizes the maturity date for debt securities.

(in millions)	December 31, 2017
Due in one year or less	$	117
Due after one through five years	552
Due after five through 10 years	554
Due after 10 years	1,061
Total	$	2,284

Schedule of Realized Gain (Loss)

Realized gains and losses, which were determined on a specific identification basis, from sales of AFS securities were as follows.

	Years Ended December 31,
(in millions)	2017		2016		2015
Realized gains	$	202	$	246	$	193
Realized losses	160		187		98

Duke Energy Carolinas [Member]

Schedule of Available-for-sale Securities [Line Items]

Available-For-Sale Investments

The following table presents the estimated fair value of investments in AFS securities.

	December 31, 2017						December 31, 2016
	Gross		Gross				Gross		Gross
	Unrealized		Unrealized				Unrealized		Unrealized
	Holding		Holding		Estimated		Holding		Holding		Estimated
(in millions)	Gains		Losses		Fair Value		Gains		Losses(a)		Fair Value
NDTF
Cash and cash equivalents	$	—	$	—	$	32	$	—	$	—	$	18
Equity securities	1,531		12		2,692		1,157		28		2,245
Corporate debt securities	9		2		359		5		6		354
Municipal bonds	—		1		60		1		2		67
U.S. government bonds	3		4		503		2		5		458
Other debt securities	—		1		112		—		3		116
Total NDTF	$	1,543	$	20	$	3,758	$	1,165	$	44	$	3,258
Other Investments
Other debt securities	$	—	$	—	$	—	$	—	$	1	$	3
Total Other Investments	$	—	$	—	$	—	$	—	$	1	$	3
Total Investments	$	1,543	$	20	$	3,758	$	1,165	$	45	$	3,261

Investments Classified by Contractual Maturity Date

The table below summarizes the maturity date for debt securities.

(in millions)	December 31, 2017
Due in one year or less	$	9
Due after one through five years	204
Due after five through 10 years	300
Due after 10 years	521
Total	$	1,034

Schedule of Realized Gain (Loss)

Realized gains and losses, which were determined on a specific identification basis, from sales of AFS securities were as follows.

	Years Ended December 31,
(in millions)	2017		2016		2015
Realized gains	$	135	$	157	$	158
Realized losses	103		121		83

Progress Energy [Member]

Schedule of Available-for-sale Securities [Line Items]

Available-For-Sale Investments

The following table presents the estimated fair value of investments in AFS securities.

	December 31, 2017						December 31, 2016
	Gross		Gross				Gross		Gross
	Unrealized		Unrealized				Unrealized		Unrealized
	Holding		Holding		Estimated		Holding		Holding		Estimated
(in millions)	Gains		Losses		Fair Value		Gains		Losses(a)		Fair Value
NDTF
Cash and cash equivalents	$	—	$	—	$	83	$	—	$	—	$	93
Equity securities	1,274		15		2,222		935		26		1,861
Corporate debt securities	8		—		211		5		2		174
Municipal bonds	4		2		284		2		8		264
U.S. government bonds	8		3		524		8		3		526
Other debt securities	—		—		6		—		—		8
Total NDTF	$	1,294	$	20	$	3,330	$	950	$	39	$	2,926
Other Investments
Cash and cash equivalents	$	—	$	—	$	12	$	—	$	—	$	21
Municipal bonds	2		—		47		2		—		44
Total Other Investments	$	2	$	—	$	59	$	2	$	—	$	65
Total Investments	$	1,296	$	20	$	3,389	$	952	$	39	$	2,991

Investments Classified by Contractual Maturity Date

The table below summarizes the maturity date for debt securities.

(in millions)	December 31, 2017
Due in one year or less	$	94
Due after one through five years	301
Due after five through 10 years	203
Due after 10 years	474
Total	$	1,072

Schedule of Realized Gain (Loss)

Realized gains and losses, which were determined on a specific identification basis, from sales of AFS securities were as follows.

	Years Ended December 31,
(in millions)	2017		2016		2015
Realized gains	$	65	$	84	$	33
Realized losses	56		64		13

Duke Energy Progress [Member]

Schedule of Available-for-sale Securities [Line Items]

Available-For-Sale Investments

The following table presents the estimated fair value of investments in AFS securities.

	December 31, 2017						December 31, 2016
	Gross		Gross				Gross		Gross
	Unrealized		Unrealized				Unrealized		Unrealized
	Holding		Holding		Estimated		Holding		Holding		Estimated
(in millions)	Gains		Losses		Fair Value		Gains		Losses(a)		Fair Value
NDTF
Cash and cash equivalents	$	—	$	—	$	50	$	—	$	—	$	45
Equity securities	980		12		1,795		704		21		1,505
Corporate debt securities	6				149		4		1		120
Municipal bonds	4		2		283		2		8		263
U.S. government bonds	5		2		310		5		2		275
Other debt securities	—		—		4		—		—		5
Total NDTF	$	995	$	16	$	2,591	$	715	$	32	$	2,213
Other Investments
Cash and cash equivalents	$	—	$	—	$	1	$	—	$	—	$	1
Total Other Investments	$	—	$	—	$	1	$	—	$	—	$	1
Total Investments	$	995	$	16	$	2,592	$	715	$	32	$	2,214

Investments Classified by Contractual Maturity Date

The table below summarizes the maturity date for debt securities.

(in millions)	December 31, 2017
Due in one year or less	$	21
Due after one through five years	219
Due after five through 10 years	146
Due after 10 years	360
Total	$	746

Schedule of Realized Gain (Loss)

Realized gains and losses, which were determined on a specific identification basis, from sales of AFS securities were as follows.

	Years Ended December 31,
(in millions)	2017		2016		2015
Realized gains	$	54	$	71	$	26
Realized losses	48		55		11

Duke Energy Florida [Member]

Schedule of Available-for-sale Securities [Line Items]

Available-For-Sale Investments

The following table presents the estimated fair value of investments in AFS securities.

	December 31, 2017						December 31, 2016
	Gross		Gross				Gross		Gross
	Unrealized		Unrealized				Unrealized		Unrealized
	Holding		Holding		Estimated		Holding		Holding		Estimated
(in millions)	Gains		Losses		Fair Value		Gains		Losses(a)		Fair Value
NDTF
Cash and cash equivalents	$	—	$	—	$	33	$	—	$	—	$	48
Equity securities	294		3		427		231		5		356
Corporate debt securities	2		—		62		1		1		54
Municipal bonds	—		—		1		—		—		1
U.S. government bonds	3		1		214		3		1		251
Other debt securities	—		—		2		—		—		3
Total NDTF(a)	$	299	$	4	$	739	$	235	$	7	$	713
Other Investments
Cash and cash equivalents	$	—	$	—	$	1	$	—	$	—	$	4
Municipal bonds	2		—		47		2		—		44
Total Other Investments	$	2	$	—	$	48	$	2	$	—	$	48
Total Investments	$	301	$	4	$	787	$	237	$	7	$	761

(a) During the year ended December 31, 2017, Duke Energy Florida continued to receive reimbursements from the NDTF for costs related to ongoing decommissioning activity of the Crystal River Unit 3 nuclear plant.

Investments Classified by Contractual Maturity Date

The table below summarizes the maturity date for debt securities.

(in millions)	December 31, 2017
Due in one year or less	$	73
Due after one through five years	82
Due after five through 10 years	57
Due after 10 years	114
Total	$	326

Schedule of Realized Gain (Loss)

Realized gains and losses, which were determined on a specific identification basis, from sales of AFS securities were as follows.

	Years Ended December 31,
(in millions)	2017		2016		2015
Realized gains	$	11	$	13	$	7
Realized losses	8		9		2

Duke Energy Indiana [Member]

Schedule of Available-for-sale Securities [Line Items]

Available-For-Sale Investments

The following table presents the estimated fair value of investments in AFS securities.

	December 31, 2017						December 31, 2016
	Gross		Gross				Gross		Gross
	Unrealized		Unrealized				Unrealized		Unrealized
	Holding		Holding		Estimated		Holding		Holding		Estimated
(in millions)	Gains		Losses		Fair Value		Gains		Losses(a)		Fair Value
Other Investments
Equity securities	$	49	$	—	$	97	$	33	$	—	$	79
Corporate debt securities	—		—		3		—		—		2
Municipal bonds	—		1		28		—		1		28
U.S. government bonds	—		—		—		—		—		1
Total Other Investments	$	49	$	1	$	128	$	33	$	1	$	110
Total Investments	$	49	$	1	$	128	$	33	$	1	$	110

Investments Classified by Contractual Maturity Date

The table below summarizes the maturity date for debt securities.

(in millions)	December 31, 2017
Due in one year or less	$	5
Due after one through five years	12
Due after five through 10 years	7
Due after 10 years	7
Total	$	31