Year Ended December 31,
2019
2018
2017
Service cost
$9.4
$9.6
$10.0
Interest cost
5.0
4.7
4.3
Expected return on plan assets
(6.0)
(6.1)
(5.5)
Curtailment gain
—
(0.3)
—
Actuarial and other loss
15.6
6.1
1.9
Total net periodic pension cost
$24.0
$14.0
$10.7
Weighted average assumptions
Discount rate used for net periodic pension costs
1.74 %
1.66 %
1.60 %
Discount rate used for pension benefit obligations
1.43 %
1.74 %
1.66 %
Expected return on plan assets
3.23 %
3.18 %
3.22 %
Rate of compensation increase
3.07 %
3.22 %
3.22 %

text: Defined Benefit Pension Plans
text: The Company maintains defined benefit pension plans for employees of certain of its foreign subsidiaries. Such plans conform to local practice in terms of providing minimum benefits mandated by law, collective agreements or customary practice. The Company recognizes the aggregate amount of all overfunded plans as assets and the aggregate amount of all underfunded plans as liabilities in its financial statements.
text: The Company's expected long-term rate of return on plan assets is updated at least annually, taking into consideration its asset allocation, historical returns on similar types of assets and the current economic environment. For estimation purposes, the Company assumes its long-term asset mix will generally be consistent with the current mix. The Company determines its discount rates using highly rated corporate bond yields and government bond yields.
text: Benefits under all of the Company's plans are valued utilizing the projected unit credit cost method. The Company's policy is to fund its defined benefit plans in accordance with local requirements and regulations. The funding is primarily driven by the Company's current assessment of the economic environment and projected benefit payments of its foreign subsidiaries. The Company's measurement date for determining its defined benefit obligations for all plans is December 31 of each year.
text: The Company recognizes actuarial gains and losses in the period the Company's annual pension plan actuarial valuations are prepared, which generally occurs during the fourth quarter of each year, or during any interim period where a revaluation is deemed necessary.
text: The following is a summary of the status of the Company's foreign defined benefit pension plans and the net periodic pension cost (dollars in millions):
text: The long term rate of return on plan assets was determined using the weighted-average method, which incorporates factors that include the historical inflation rates, interest rate yield curve and current market conditions.

Questions:
question: What is the service cost in 2019?
answer: $9.4
scale: million
question: What is the service cost in 2018?
answer: $9.6
scale: million
question: What is the interest cost in 2018?
answer: 4.7
scale: million
question: What is the change in Service cost from December 31, 2018 to 2019?
answer: -0.2
derivation: 9.4-9.6
scale: million
question: What is the change in Interest cost from year ended December 31, 2018 to 2019?
answer: 0.3
derivation: 5.0-4.7
scale: million
question: What is the average Service cost for December 31, 2018 and 2019?
answer: 9.5
derivation: (9.4+9.6) / 2
scale: million