Benefit Plans and Other Postretirement Benefits (Tables)

6 Months Ended

Jun. 30, 2018

Retirement Benefits [Abstract]

Components of Net Periodic Benefit Cost

Components of Net Periodic Benefit Cost

	Three Months Ended June 30
	2018			2017			2018			2017
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	1,194		$	1,155		$	9		$	7
Interest cost (a)	1,360			1,555			142			148
Expected return on plan assets (a)	(2,257		)	(2,295		)	(16		)	(8		)
Amortization of prior service (credit) cost (a)	(6		)	34			(88		)	(88		)
Amortization of net loss (a)	1,419			1,461			139			109
Net periodic benefit cost	1,710			1,910			186			168
Costs not recognized due to the effects of regulation	—			—			—			—
Net benefit cost recognized for financial reporting	$	1,710		$	1,910		$	186		$	168

	Six Months Ended June 30
	2018			2017			2018			2017
(Thousands of Dollars)	Pension Benefits						Postretirement Health Care Benefits
Service cost	$	2,389		$	2,309		$	18		$	14
Interest cost (a)	2,720			3,109			284			296
Expected return on plan assets (a)	(4,513		)	(4,590		)	(32		)	(16		)
Amortization of prior service (credit) cost (a)	(14		)	69			(176		)	(176		)
Amortization of net loss (a)	2,837			2,923			278			218
Net periodic benefit cost	3,419			3,820			372			336
Credits not recognized due to the effects of regulation	221			—			—			—
Net benefit cost recognized for financial reporting	$	3,640		$	3,820		$	372		$	336

^(a) The components of net periodic cost other than the service cost component are included in the line item “other expense, net” in the income statement or capitalized on the balance sheet as a regulatory asset.