Retirement Plans and Other Postretirement Benefits (Tables)

3 Months Ended

Mar. 31, 2022

Schedule of net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction, billed to electric plant participants or charged or amortized to the regulatory asset)

The following table provides details of the plans’ net periodic benefit costs and the portion of these costs charged to expense (including administrative costs and excluding amounts capitalized as overhead construction or billed to electric plant participants) (dollars in thousands):


	Pension Benefits				Other Benefits
	Three Months Ended March 31,					Three Months Ended March 31,
	2022		2021				2022		2021
Service cost — benefits earned during the period	$	14,331	$	15,679			$	4,218	$	4,557
Non-service costs (credits):
Interest cost on benefit obligation	27,023		24,669				4,463		4,162
Expected return on plan assets	(46,394)		(50,608)				(11,510)		(10,361)
Amortization of:
Prior service credit	—		—				(9,447)		(9,427)
Net actuarial loss (gain)	4,768		3,985				(2,982)		(2,405)
Net periodic benefit	$	(272)	$	(6,275)			$	(15,258)	$	(13,474)
Portion of benefit charged to expense	$	(3,290)	$	(8,011)			$	(10,895)	$	(9,528)