9. RETIREMENT BENEFITS

The cost to the company of its retirement plans is shown in the following table:



	Three Months Ended June 30												Six Months Ended June 30
	Pension Benefits						Medical and Life Benefits						Pension Benefits						Medical and Life Benefits
$ in millions	2018			2017			2018			2017			2018			2017			2018			2017
Components of net periodic benefit cost
Service cost	$	100		$	97		$	5		$	6		$	199		$	194		$	10		$	11
Interest cost	300			312			19			21			590			625			38			42
Expected return on plan assets	(544		)	(472		)	(24		)	(23		)	(1,073		)	(943		)	(49		)	(45		)
Amortization of:
Prior service credit	(14		)	(14		)	(6		)	(6		)	(29		)	(29		)	(11		)	(11		)
Net loss from previous years	133			191			—			4			267			382			—			7
Net periodic benefit cost	$	(25	)	$	114		$	(6	)	$	2		$	(46	)	$	229		$	(12	)	$	4

Changes in Presentation

As discussed in Note 1, we adopted ASU 2017-07 on January 1, 2018 using the retrospective method, which changed the financial statement presentation of service costs and the other components of net periodic benefit cost. The service cost component continues to be included in operating income; however, the other components are now presented in Net FAS (non-service) pension benefit (expense) in the unaudited condensed consolidated statements of earnings and comprehensive income. In addition, interest on service cost and plan administrative expenses which, in some cases, have historically been included in service cost are now consistently presented in the interest cost and amortization of net actuarial loss components, respectively. As a result, the company reclassified interest on service cost of $4 million and $8 million and plan administrative expenses of $13 million and $26 million from service cost to the interest cost and amortization of net actuarial loss components, respectively, for its pension plans in the three and six months ended June 30, 2017, respectively, to conform to the current year presentation. For the company’s medical and life benefit plans, plan administrative expenses of $1 million and $2 million were reclassified from service cost to the amortization of net actuarial loss component for the three and six months ended June 30, 2017, respectively, to conform to the current year presentation. This change in presentation had no impact on net periodic benefit cost.

Employer Contributions

The company sponsors defined benefit pension and post-retirement plans, as well as defined contribution plans. We fund our defined benefit pension plans annually in a manner consistent with the Employee Retirement Income Security Act of 1974, as amended by the Pension Protection Act of 2006, including making voluntary contributions from time to time.

Contributions made by the company to its retirement plans are as follows:



	Three Months Ended June 30				Six Months Ended June 30
$ in millions	2018		2017		2018		2017
Defined benefit pension plans	$	23	$	28	$	45	$	51
Medical and life benefit plans	11		13		22		24
Defined contribution plans	88		77		192		176