The service cost component of net periodic benefit costs included in the table below are components of an overhead loading process associated with the cost of labor (refer to discussion above related to the update to Topic 715). The overhead process ultimately results in allocation of that portion of overall net periodic benefit costs to the same accounts to which productive labor is charged. As a result, service costs become components of various accounts, primarily operations and maintenance expense, net utility plant, and deferred charges and other assets for both the Company and Southwest. Refer also to the practical expedient elected related to amounts capitalized as part of assets prior to the adoption date.



	Qualified Retirement Plan
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2018			2017			2018			2017			2018			2017
(Thousands of dollars)
Service cost	$	7,139		$	5,848		$	21,417		$	17,544		$	27,265		$	23,252
Interest cost	11,043			11,520			33,130			34,561			44,652			46,068
Expected return on plan assets	(14,689		)	(13,799		)	(44,066		)	(41,397		)	(57,865		)	(55,536		)
Amortization of net actuarial loss	8,029			6,001			24,086			18,003			30,087			24,319
Net periodic benefit cost	$	11,522		$	9,570		$	34,567		$	28,711		$	44,139		$	38,103

	SERP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2018			2017			2018			2017			2018			2017
(Thousands of dollars)
Service cost	$	61		$	77		$	183		$	232		$	260		$	315
Interest cost	415			471			1,244			1,413			1,714			1,878
Amortization of net actuarial loss	375			361			1,126			1,081			1,486			1,426
Net periodic benefit cost	$	851		$	909		$	2,553		$	2,726		$	3,460		$	3,619

	PBOP
	Period Ended September 30,
	Three Months						Nine Months						Twelve Months
	2018			2017			2018			2017			2018			2017
(Thousands of dollars)
Service cost	$	368		$	367		$	1,105		$	1,101		$	1,472		$	1,476
Interest cost	687			808			2,061			2,424			2,869			3,218
Expected return on plan assets	(929		)	(839		)	(2,789		)	(2,518		)	(3,629		)	(3,305		)
Amortization of prior service costs	334			333			1,002			1,001			1,336			1,335
Amortization of net actuarial loss	—			—			—			—			—			105
Net periodic benefit cost	$	460		$	669		$	1,379		$	2,008		$	2,048		$	2,829