Benefit Plans (Tables)

9 Months Ended

Sep. 30, 2017

Components of Net Periodic Benefit Cost

AEP

	Pension Plans						Other Postretirement Benefit Plans
	Three Months Ended September 30,						Three Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	24.1		$	21.4		$	2.8		$	2.6
Interest Cost	50.7			52.9			14.8			15.3
Expected Return on Plan Assets	(71.1		)	(70.1		)	(25.3		)	(26.8		)
Amortization of Prior Service Cost (Credit)	0.3			0.6			(17.3		)	(17.3		)
Amortization of Net Actuarial Loss	20.7			21.0			9.2			7.8
Net Periodic Benefit Cost (Credit)	$	24.7		$	25.8		$	(15.8	)	$	(18.4	)

	Pension Plans						Other Postretirement Benefit Plans
	Nine Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	72.3		$	64.3		$	8.4		$	7.7
Interest Cost	152.3			158.7			44.5			45.7
Expected Return on Plan Assets	(213.5		)	(210.2		)	(76.0		)	(80.3		)
Amortization of Prior Service Cost (Credit)	0.8			1.7			(51.8		)	(51.8		)
Amortization of Net Actuarial Loss	62.1			62.9			27.5			23.5
Net Periodic Benefit Cost (Credit)	$	74.0		$	77.4		$	(47.4	)	$	(55.2	)

Appalachian Power Co [Member]

Components of Net Periodic Benefit Cost

APCo

	Pension Plans						Other Postretirement Benefit Plans
	Three Months Ended September 30,						Three Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	2.3		$	2.1		$	0.3		$	0.2
Interest Cost	6.5			6.8			2.6			2.7
Expected Return on Plan Assets	(8.9		)	(8.8		)	(4.1		)	(4.3		)
Amortization of Prior Service Credit	—			—			(2.5		)	(2.5		)
Amortization of Net Actuarial Loss	2.6			2.6			1.6			1.4
Net Periodic Benefit Cost (Credit)	$	2.5		$	2.7		$	(2.1	)	$	(2.5	)

	Pension Plans						Other Postretirement Benefit Plans
	Nine Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	7.0		$	6.1		$	0.8		$	0.7
Interest Cost	19.3			20.4			7.9			8.1
Expected Return on Plan Assets	(26.8		)	(26.5		)	(12.3		)	(13.0		)
Amortization of Prior Service Cost (Credit)	0.1			0.1			(7.5		)	(7.5		)
Amortization of Net Actuarial Loss	7.8			8.0			4.7			4.1
Net Periodic Benefit Cost (Credit)	$	7.4		$	8.1		$	(6.4	)	$	(7.6	)

Indiana Michigan Power Co [Member]

Components of Net Periodic Benefit Cost

I&M

	Pension Plans						Other Postretirement Benefit Plans
	Three Months Ended September 30,						Three Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	3.5		$	3.1		$	0.4		$	0.4
Interest Cost	6.1			6.3			1.7			1.7
Expected Return on Plan Assets	(8.6		)	(8.4		)	(3.1		)	(3.2		)
Amortization of Prior Service Credit	—			—			(2.3		)	(2.4		)
Amortization of Net Actuarial Loss	2.4			2.5			1.1			0.9
Net Periodic Benefit Cost (Credit)	$	3.4		$	3.5		$	(2.2	)	$	(2.6	)

	Pension Plans						Other Postretirement Benefit Plans
	Nine Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	10.5		$	9.2		$	1.2		$	1.1
Interest Cost	18.2			19.0			5.2			5.2
Expected Return on Plan Assets	(25.9		)	(25.2		)	(9.2		)	(9.6		)
Amortization of Prior Service Cost (Credit)	0.1			0.1			(7.0		)	(7.1		)
Amortization of Net Actuarial Loss	7.3			7.4			3.3			2.8
Net Periodic Benefit Cost (Credit)	$	10.2		$	10.5		$	(6.5	)	$	(7.6	)

Ohio Power Co [Member]

Components of Net Periodic Benefit Cost

OPCo

	Pension Plans						Other Postretirement Benefit Plans
	Three Months Ended September 30,						Three Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	1.8		$	1.6		$	0.3		$	0.2
Interest Cost	4.8			5.1			1.6			1.8
Expected Return on Plan Assets	(6.9		)	(6.9		)	(3.0		)	(3.3		)
Amortization of Prior Service Credit	—			—			(1.7		)	(1.7		)
Amortization of Net Actuarial Loss	2.0			2.1			1.1			0.9
Net Periodic Benefit Cost (Credit)	$	1.7		$	1.9		$	(1.7	)	$	(2.1	)

	Pension Plans						Other Postretirement Benefit Plans
	Nine Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	5.6		$	4.9		$	0.7		$	0.6
Interest Cost	14.5			15.4			5.0			5.3
Expected Return on Plan Assets	(20.9		)	(20.8		)	(9.0		)	(9.7		)
Amortization of Prior Service Cost (Credit)	0.1			0.1			(5.2		)	(5.2		)
Amortization of Net Actuarial Loss	5.9			6.1			3.3			2.8
Net Periodic Benefit Cost (Credit)	$	5.2		$	5.7		$	(5.2	)	$	(6.2	)

Public Service Co Of Oklahoma [Member]

Components of Net Periodic Benefit Cost

PSO

	Pension Plans						Other Postretirement Benefit Plans
	Three Months Ended September 30,						Three Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	1.7		$	1.5		$	0.2		$	0.2
Interest Cost	2.6			2.8			0.8			0.8
Expected Return on Plan Assets	(3.9		)	(3.9		)	(1.4		)	(1.5		)
Amortization of Prior Service Cost (Credit)	—			0.1			(1.1		)	(1.1		)
Amortization of Net Actuarial Loss	1.1			1.1			0.5			0.4
Net Periodic Benefit Cost (Credit)	$	1.5		$	1.6		$	(1.0	)	$	(1.2	)

	Pension Plans						Other Postretirement Benefit Plans
	Nine Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	4.9		$	4.6		$	0.5		$	0.5
Interest Cost	8.0			8.4			2.4			2.4
Expected Return on Plan Assets	(11.8		)	(11.6		)	(4.2		)	(4.5		)
Amortization of Prior Service Cost (Credit)	—			0.2			(3.2		)	(3.2		)
Amortization of Net Actuarial Loss	3.3			3.3			1.5			1.3
Net Periodic Benefit Cost (Credit)	$	4.4		$	4.9		$	(3.0	)	$	(3.5	)

Southwestern Electric Power Co [Member]

Components of Net Periodic Benefit Cost

SWEPCo

	Pension Plans						Other Postretirement Benefit Plans
	Three Months Ended September 30,						Three Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	2.1		$	2.0		$	0.2		$	0.2
Interest Cost	3.1			3.1			0.9			0.9
Expected Return on Plan Assets	(4.2		)	(4.0		)	(1.5		)	(1.7		)
Amortization of Prior Service Credit	—			—			(1.3		)	(1.3		)
Amortization of Net Actuarial Loss	1.3			1.2			0.5			0.5
Net Periodic Benefit Cost (Credit)	$	2.3		$	2.3		$	(1.2	)	$	(1.4	)

	Pension Plans						Other Postretirement Benefit Plans
	Nine Months Ended September 30,						Nine Months Ended September 30,
	2017			2016			2017			2016
	(in millions)
Service Cost	$	6.5		$	6.1		$	0.6		$	0.6
Interest Cost	9.2			9.3			2.7			2.7
Expected Return on Plan Assets	(12.6		)	(12.3		)	(4.7		)	(5.0		)
Amortization of Prior Service Cost (Credit)	—			0.2			(3.9		)	(3.9		)
Amortization of Net Actuarial Loss	3.7			3.6			1.7			1.5
Net Periodic Benefit Cost (Credit)	$	6.8		$	6.9		$	(3.6	)	$	(4.1	)