18. Retirement and Employee Benefit Plans

We have defined contribution plans covering certain employees. Contribution expenses related to these plans totaled $37 million, $24 million and $30 million in 2018, 2017 and 2016, respectively. The increase in employer contributions in 2018 relates primarily to the recommencement of employer matching contributions to our U.S. 401(k) savings plan and other contribution plans sponsored by the Company. The decrease in 2017 relates primarily to headcount reductions and the suspension of employer matching contributions.

We have defined benefit pension and other post-retirement benefit plans covering certain U.S. and international employees. Plan benefits are generally based on factors such as age, compensation levels and years of service. Net periodic benefit income/cost related to these plans totaled $8 million of cost in 2018, $38 million of income in 2017 and $9 million of cost in 2016. The change in net periodic benefit income/cost is due primarily to amortization of the unrecognized net gain associated with our supplemental executive retirement plan in 2017. The projected benefit obligations on a consolidated basis were $173 million and $198 million as of December 31, 2018 and 2017, respectively. The decrease year over year is due primarily to actuarial gains and currency fluctuations. The fair values of plan assets on a consolidated basis (determined primarily using Level 2 inputs) were $123 million and $133 million as of December 31, 2018 and 2017, respectively. The decrease in plan assets year over year is due primarily to negative asset returns and currency fluctuations. As of December 31, 2018 and December 31, 2017, the net underfunded obligation was substantially all recorded within Other Non-current Liabilities. Additionally, consolidated pre-tax amounts in accumulated other comprehensive loss that have not yet been recognized as components of net periodic benefit cost were a net loss of $21 million and loss of $35 million as of December 31, 2018 and 2017, respectively. The change in other comprehensive loss year over year is due primarily to net actuarial gains.

The weighted average assumption rates used for benefit obligations were as follows:



	Year Ended December 31,
	2018	2017
Discount rate:
United States Plans	3.00% - 4.25%	3.00% - 3.50%
International Plans	1.85% - 7.25%	1.60% - 6.75%
Rate of Compensation Increase:
United States Plans	—	—
International Plans	2.00% - 3.50%	2.00% - 3.50%

During 2018 and 2017, we made contributions and paid direct benefits of $5 million and $23 million, respectively, in connection with our defined benefit pension and other post-retirement benefit plans. In 2019, we expect to fund approximately $5 million related to those plans.