Retirement Benefits

Components of retirement benefits expense (income) are:



	Pension Benefits						Postretirement Medical and Life Insurance Benefits
	Three months ended June 30,
	2018			2017			2018			2017
	(In millions)
Interest cost on benefit obligation	$	12.5		$	14.4		$	0.3		$	0.3
Assumed return on plan assets	(15.1		)	(12.4		)	—			—
Amortization of prior service costs	0.1			0.1			—			—
Recognized net actuarial losses (gains)	17.6			16.9			(1.0		)	(1.0		)
Retirement benefits expense (income)	$	15.1		$	19.0		$	(0.7	)	$	(0.7	)



	Pension Benefits						Postretirement Medical and Life Insurance Benefits
	Six months ended June 30,
	2018			2017			2018			2017
	(In millions)
Interest cost on benefit obligation	$	24.9		$	28.8		$	0.6		$	0.7
Assumed return on plan assets	(30.1		)	(24.8		)	—			—
Amortization of prior service costs (credits)	0.1			0.1			(0.1		)	(0.1		)
Recognized net actuarial losses (gains)	35.3			33.9			(1.9		)	(2.0		)
Retirement benefits expense (income)	$	30.2		$	38.0		$	(1.4	)	$	(1.4	)

Service costs represent the annual growth in benefits earned by participants during the year. Since the Company’s defined benefit pension plan future benefit accrual is discontinued for all participants, the Company has determined in connection with the adoption of accounting guidance on presentation of service cost and other components of retirement benefits expense that the service cost is zero for all periods presented. Historically, the Company has included expenses paid from the tax-qualified defined benefit pension plan trust, including Public Benefit Guaranty Corporation, audit, actuarial, legal and administrative fees, as service costs in the presentation of the components of retirement benefits expense (income). The Company determined that the vast majority of these types of expenses reflect a reduction to the assumed return on plan assets because they reduce the expected growth of the plan assets. As such, the Company has elected to reclassify the trust-paid expenses related to the tax-qualified defined benefit pension plan as a reduction to assumed return on plan assets for all periods presented. For the three and six months ended June 30, 2017, the Company has reclassified expenses of $3.8 million and $7.5 million, respectively, from service cost to assumed return on plan assets in the table above. This change in presentation had no impact on net retirement benefits expense (income).