Employee Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2018

Defined Benefit Plan Disclosure [Line Items]

Defined Contribution Plan Disclosures

The following table includes employer contributions made by Duke Energy and expensed by the Subsidiary Registrants.

			Duke				Duke		Duke		Duke		Duke
	Duke		Energy		Progress		Energy		Energy		Energy		Energy
(in millions)	Energy		Carolinas		Energy		Progress		Florida		Ohio		Indiana		Piedmont
Three Months Ended March 31,
2018	$	70	$	23	$	19	$	13	$	6	$	1	$	3	$	4
2017	65		22		18		13		5		1		3		2

Qualified Pension Plan [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule of Defined Benefit Plans Disclosures

The following table includes information related to the Duke Energy Registrants' contributions to its qualified defined benefit pension plans.

			Duke				Duke		Duke		Duke		Duke
	Duke		Energy		Progress		Energy		Energy		Energy		Energy
(in millions)	Energy		Carolinas		Energy		Progress		Florida		Ohio		Indiana		Piedmont
Total anticipated 2018 contributions	$	148	$	46	$	45	$	25	$	20	$	—	$	8	$	7
Contributions made during the three months ended March 31, 2018	141		46		45		25		20		—		8		—
Remaining estimated 2018 contributions	$	7	$	—	$	—	$	—	$	—	$	—	$	—	$	7

Components of Net Periodic Pension Costs

The following tables include the components of net periodic pension costs for qualified pension plans.

	Three Months Ended March 31, 2018
				Duke						Duke			Duke			Duke			Duke
	Duke			Energy			Progress			Energy			Energy			Energy			Energy
(in millions)	Energy			Carolinas			Energy			Progress			Florida			Ohio			Indiana			Piedmont
Service cost	$	45		$	15		$	13		$	7		$	5		$	1		$	2		$	2
Interest cost on projected benefit obligation	75			18			24			11			13			5			6			3
Expected return on plan assets	(140		)	(37		)	(45		)	(21		)	(23		)	(7		)	(10		)	(6		)
Amortization of actuarial loss	33			7			11			5			6			1			2			3
Amortization of prior service credit	(8		)	(2		)	(1		)	—			—			—			—			(3		)
Net periodic pension costs	$	5		$	1		$	2		$	2		$	1		$	—		$	—		$	(1	)

	Three Months Ended March 31, 2017
				Duke						Duke			Duke			Duke			Duke
	Duke			Energy			Progress			Energy			Energy			Energy			Energy
(in millions)	Energy			Carolinas			Energy			Progress			Florida			Ohio			Indiana			Piedmont
Service cost	$	40		$	12		$	12		$	6		$	5		$	1		$	2		$	3
Interest cost on projected benefit obligation	82			20			25			12			13			5			7			3
Expected return on plan assets	(136		)	(35		)	(43		)	(21		)	(21		)	(7		)	(11		)	(6		)
Amortization of actuarial loss	36			8			14			6			7			1			3			3
Amortization of prior service credit	(6		)	(2		)	(1		)	—			—			—			—			(1		)
Other	2			—			1			—			—			—			—			—
Net periodic pension costs	$	18		$	3		$	8		$	3		$	4		$	—		$	1		$	2

Other Post-Retirement Benefit Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

Components of Net Periodic Pension Costs

The following tables include the components of net periodic other post-retirement benefit costs.

	Three Months Ended March 31, 2018
				Duke						Duke		Duke			Duke		Duke
	Duke			Energy			Progress			Energy		Energy			Energy		Energy
(in millions)	Energy			Carolinas			Energy			Progress		Florida			Ohio		Indiana		Piedmont
Service cost	$	1		$	—		$	—		$	—	$	—		$	—	$	—	$	—
Interest cost on accumulated post-retirement benefit obligation	7			2			4			1		1			—		1		—
Expected return on plan assets	(2		)	(2		)	—			—		—			—		—		—
Amortization of actuarial loss	1			—			—			—		—			—		1		—
Amortization of prior service credit	(5		)	(1		)	(2		)	—		(1		)	—		—		—
Net periodic other post-retirement benefit costs	$	2		$	(1	)	$	2		$	1	$	—		$	—	$	2	$	—

	Three Months Ended March 31, 2017
				Duke						Duke			Duke			Duke		Duke
	Duke			Energy			Progress			Energy			Energy			Energy		Energy
(in millions)	Energy			Carolinas			Energy			Progress			Florida			Ohio		Indiana		Piedmont
Service cost	$	1		$	—		$	—		$	—		$	—		$	—	$	—	$	—
Interest cost on accumulated post-retirement benefit obligation	9			2			4			2			2			—		—		—
Expected return on plan assets	(3		)	(2		)	—			—			—			—		—		—
Amortization of actuarial loss (gain)	2			(1		)	5			3			2			—		—		—
Amortization of prior service credit	(29		)	(2		)	(21		)	(14		)	(8		)	—		—		—
Net periodic other post-retirement benefit costs	$	(20	)	$	(3	)	$	(12	)	$	(9	)	$	(4	)	$	—	$	—	$	—