Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Measurement Amounts For Assets And Liabilities

The following tables provide recorded balances for assets and liabilities measured at fair value on a recurring basis on the Consolidated Balance Sheets. Derivative amounts in the table below for all Duke Energy Registrants exclude cash collateral, which is disclosed in Note 14. See Note 15 for additional information related to investments by major security type for the Duke Energy Registrants.

	December 31, 2017
(in millions)	Total Fair Value			Level 1			Level 2			Level 3			Not Categorized
NDTF equity securities	$	4,914		$	4,840		$	—		$	—		$	74
NDTF debt securities	2,174			635			1,539			—			—
Other AFS equity securities	123			123			—			—			—
Other trading and AFS debt securities	241			57			184			—			—
Derivative assets	51			3			20			28			—
Total assets	7,503			5,658			1,743			28			74
Derivative liabilities	(230		)	(2		)	(86		)	(142		)	—
Net assets (liabilities)	$	7,273		$	5,656		$	1,657		$	(114	)	$	74

	December 31, 2016
(in millions)	Total Fair Value			Level 1			Level 2			Level 3			Not Categorized
NDTF equity securities	$	4,106		$	4,029		$	—		$	—		$	77
NDTF debt securities	2,078			632			1,446			—			—
Other trading and AFS equity securities	104			104			—			—			—
Other trading and AFS debt securities	266			75			186			5			—
Derivative assets	162			5			136			21			—
Total assets	6,716			4,845			1,768			26			77
Derivative liabilities	(252		)	(2		)	(63		)	(187		)	—
Net assets	$	6,464		$	4,843		$	1,705		$	(161	)	$	77

Reconciliation Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs

The following tables provide reconciliations of beginning and ending balances of assets and liabilities measured at fair value using Level 3 measurements. Amounts included in earnings for derivatives are primarily included in Cost of natural gas on the Duke Energy Registrants' Consolidated Statements of Operations and Comprehensive Income. Amounts included in changes of net assets on the Duke Energy Registrants' Consolidated Balance Sheets are included in regulatory assets or liabilities. All derivative assets and liabilities are presented on a net basis.

	December 31, 2017									December 31, 2016
(in millions)	Investments			Derivatives (net)			Total			Investments		Derivatives (net)			Total
Balance at beginning of period	$	5		$	(166	)	$	(161	)	$	5	$	10		$	15
Total pretax realized or unrealized gains included in comprehensive income	1			—			1			—		—			—
Derivative liability resulting from the acquisition of Piedmont	—			—			—			—		(187		)	(187		)
Purchases, sales, issuances and settlements:
Purchases	—			55			55			—		33			33
Sales	(6		)	—			(6		)	—		—			—
Settlements	—			(47		)	(47		)	—		(28		)	(28		)
Total gains included on the Consolidated Balance Sheet	—			44			44			—		6			6
Balance at end of period	$	—		$	(114	)	$	(114	)	$	5	$	(166	)	$	(161	)

Quantitative Information Table - Level 3

The following tables include quantitative information about the Duke Energy Registrants' derivatives classified as Level 3.

	December 31, 2017
	Fair Value
Investment Type	(in millions)			Valuation Technique	Unobservable Input	Range
Duke Energy Ohio
FTRs	$	1		RTO auction pricing	FTR price – per MWh	$	0.07		–	$	1.41
Duke Energy Indiana
FTRs	27			RTO auction pricing	FTR price – per MWh	(0.77		)	–	7.44
Piedmont
Natural gas contracts	(142		)	Discounted cash flow	Forward natural gas curves - price per MMBtu	2.10			–	2.88
Duke Energy
Total Level 3 derivatives	$	(114	)

	December 31, 2016
	Fair Value
Investment Type	(in millions)			Valuation Technique	Unobservable Input	Range
Duke Energy Ohio
FTRs	$	5		RTO auction pricing	FTR price – per MWh	0.77		–	3.52
Duke Energy Indiana
FTRs	16			RTO auction pricing	FTR price – per MWh	(0.83	)	–	9.32
Piedmont
Natural gas contracts	(187		)	Discounted cash flow	Forward natural gas curves - price per MMBtu	2.31		–	4.18
Duke Energy
Total Level 3 derivatives	$	(166	)

Schedule of Long-term debt Fair Value

The fair value and book value of long-term debt, including current maturities, is summarized in the following table. Estimates determined are not necessarily indicative of amounts that could have been settled in current markets. Fair value of long-term debt uses Level 2 measurements.

	December 31, 2017				December 31, 2016
(in millions)	Book Value		Fair Value		Book Value		Fair Value
Duke Energy	$	52,279	$	55,331	$	47,895	$	49,161
Duke Energy Carolinas	10,103		11,372		9,603		10,494
Progress Energy	17,837		20,000		17,541		19,107
Duke Energy Progress	7,357		7,992		7,011		7,357
Duke Energy Florida	7,095		7,953		6,125		6,728
Duke Energy Ohio	2,067		2,249		1,884		2,020
Duke Energy Indiana	3,783		4,464		3,786		4,260
Piedmont	2,037		2,209		1,821		1,933

Duke Energy Carolinas [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Measurement Amounts For Assets And Liabilities

The following tables provide recorded balances for assets and liabilities measured at fair value on a recurring basis on the Consolidated Balance Sheets.

	December 31, 2017
(in millions)	Total Fair Value			Level 1			Level 2			Level 3		Not Categorized
NDTF equity securities	$	2,692		$	2,618		$	—		$	—	$	74
NDTF debt securities	1,066			204			862			—		—
Derivative assets	2			—			2			—		—
Total assets	3,760			2,822			864			—		74
Derivative liabilities	(35		)	(1		)	(34		)	—		—
Net assets	$	3,725		$	2,821		$	830		$	—	$	74

	December 31, 2016
(in millions)	Total Fair Value			Level 1		Level 2			Level 3		Not Categorized
NDTF equity securities	$	2,245		$	2,168	$	—		$	—	$	77
NDTF debt securities	1,013			178		835			—		—
Other AFS debt securities	3			—		—			3		—
Derivative assets	33			—		33			—		—
Total assets	3,294			2,346		868			3		77
Derivative liabilities	(16		)	—		(16		)	—		—
Net assets	$	3,278		$	2,346	$	852		$	3	$	77

Reconciliation Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs

The following table provides reconciliations of beginning and ending balances of assets and liabilities measured at fair value using Level 3 measurements.

	Investments
	Years Ended December 31,
(in millions)	2017			2016
Balance at beginning of period	$	3		$	3
Total pretax realized or unrealized gains included in comprehensive income	1			—
Purchases, sales, issuances and settlements:
Sales	(4		)	—
Balance at end of period	$	—		$	3

Progress Energy [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Measurement Amounts For Assets And Liabilities

The following table provides recorded balances for assets and liabilities measured at fair value on a recurring basis on the Consolidated Balance Sheets.

	December 31, 2017									December 31, 2016
(in millions)	Total Fair Value			Level 1			Level 2			Total Fair Value			Level 1		Level 2
NDTF equity securities	$	2,222		$	2,222		$	—		$	1,861		$	1,861	$	—
NDTF debt securities	1,108			431			677			1,065			454		611
Other AFS debt securities	59			12			47			65			21		44
Derivative assets	3			1			2			85			—		85
Total assets	3,392			2,666			726			3,076			2,336		740
Derivative liabilities	(36		)	(1		)	(35		)	(25		)	—		(25		)
Net assets	$	3,356		$	2,665		$	691		$	3,051		$	2,336	$	715

Duke Energy Progress [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Measurement Amounts For Assets And Liabilities

The following table provides recorded balances for assets and liabilities measured at fair value on a recurring basis on the Consolidated Balance Sheets.

	December 31, 2017									December 31, 2016
(in millions)	Total Fair Value			Level 1			Level 2			Total Fair Value			Level 1		Level 2
NDTF equity securities	$	1,795		$	1,795		$	—		$	1,505		$	1,505	$	—
NDTF debt securities	796			243			553			708			207		501
Other AFS debt securities	1			1			—			1			1		—
Derivative assets	2			1			1			46			—		46
Total assets	2,594			2,040			554			2,260			1,713		547
Derivative liabilities	(18		)	(1		)	(17		)	(7		)	—		(7		)
Net assets	$	2,576		$	2,039		$	537		$	2,253		$	1,713	$	540

Duke Energy Florida [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Measurement Amounts For Assets And Liabilities

The following table provides recorded balances for assets and liabilities measured at fair value on a recurring basis on the Consolidated Balance Sheets.

	December 31, 2017								December 31, 2016
(in millions)	Total Fair Value			Level 1		Level 2			Total Fair Value			Level 1		Level 2
NDTF equity securities	$	427		$	427	$	—		$	356		$	356	$	—
NDTF debt securities	312			188		124			357			247		110
Other AFS debt securities	48			1		47			48			4		44
Derivative assets	1			—		1			39			—		39
Total assets	788			616		172			800			607		193
Derivative liabilities	(12		)	—		(12		)	(12		)	—		(12		)
Net assets	$	776		$	616	$	160		$	788		$	607	$	181

Duke Energy Ohio [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Measurement Amounts For Assets And Liabilities

The following table provides recorded balances for assets and liabilities measured at fair value on a recurring basis on the Consolidated Balance Sheets.

	December 31, 2017								December 31, 2016
(in millions)	Total Fair Value			Level 2			Level 3		Total Fair Value			Level 2			Level 3
Derivative assets	$	1		$	—		$	1	$	5		$	—		$	5
Derivative liabilities	(5		)	(5		)	—		(6		)	(6		)	—
Net (liabilities) assets	$	(4	)	$	(5	)	$	1	$	(1	)	$	(6	)	$	5

Reconciliation Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs

The following table provides a reconciliation of beginning and ending balances of assets and liabilities measured at fair value using Level 3 measurements.

	Derivatives (net)
	Years Ended December 31,
(in millions)	2017			2016
Balance at beginning of period	$	5		$	3
Purchases, sales, issuances and settlements:
Purchases	3			5
Settlements	(4		)	(5		)
Total gains included on the Consolidated Balance Sheet	(3		)	2
Balance at end of period	$	1		$	5

Duke Energy Indiana [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Measurement Amounts For Assets And Liabilities

The following table provides recorded balances for assets and liabilities measured at fair value on a recurring basis on the Consolidated Balance Sheets.

	December 31, 2017								December 31, 2016
(in millions)	Total Fair Value		Level 1		Level 2		Level 3		Total Fair Value			Level 1			Level 2		Level 3
Other AFS equity securities	$	97	$	97	$	—	$	—	$	79		$	79		$	—	$	—
Other AFS debt securities	31		—		31		—		31			—			31		—
Derivative assets	27		—		—		27		16			—			—		16
Total assets	155		97		31		27		126			79			31		16
Derivative liabilities	—		—		—		—		(2		)	(2		)	—		—
Net assets	$	155	$	97	$	31	$	27	$	124		$	77		$	31	$	16

Reconciliation Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs

The following table provides a reconciliation of beginning and ending balances of assets and liabilities measured at fair value using Level 3 measurements.

	Derivatives (net)
	Years Ended December 31,
(in millions)	2017			2016
Balance at beginning of period	$	16		$	7
Purchases, sales, issuances and settlements:
Purchases	52			29
Settlements	(43		)	(24		)
Total gains included on the Consolidated Balance Sheet	2			4
Balance at end of period	$	27		$	16

Piedmont Natural Gas [Member]

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Fair Value Measurement Amounts For Assets And Liabilities

The following table provides recorded balances for assets and liabilities measured at fair value on a recurring basis on the Consolidated Balance Sheets.

	December 31, 2017								December 31, 2016
(in millions)	Total Fair Value			Level 1		Level 3			Total Fair Value			Level 1		Level 3
Other trading equity securities	$	—		$	—	$	—		$	4		$	4	$	—
Other trading debt securities	1			1		—			1			1		—
Derivative assets	2			2		—			3			3		—
Total assets	3			3		—			8			8		—
Derivative liabilities	(142		)	—		(142		)	(187		)	—		(187		)
Net assets	$	(139	)	$	3	$	(142	)	$	(179	)	$	8	$	(187	)

Reconciliation Of Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs

The following table provides a reconciliation of beginning and ending balances of assets and liabilities measured at fair value using Level 3 measurements.

	Derivatives (net)
	Year Ended			Two Months Ended			Year Ended
(in millions)	December 31, 2017			December 31, 2016			October 31, 2016
Balance at beginning of period	$	(187	)	$	(188	)	$	—
Total gains (losses) and settlements	45			1			(188		)
Balance at end of period	$	(142	)	$	(187	)	$	(188	)