Table:
| ($ in millions) |  |  |  |
| --- | --- | --- | --- |
| For the year ended December 31: | 2019 | 2018 | Yr.-to-Yr. Percent Change |
| Retirement-related plans—cost |  |  |  |
| Service cost | $385 | $431 | (10.7)% |
| Multi-employer plans | 32 | 38 | (16.9) |
| Cost of defined contribution plans | 1,040 | 1,024 | 1.5 |
| Total operating costs/ (income) | $1,457 | $1,494 | (2.5)% |
| Interest cost | $2,929 | $2,726 | 7.4% |
| Expected return on plan assets | (4,192) | (4,049) | 3.5 |
| Recognized actuarial losses | 1,819 | 2,941 | (38.2) |
| Amortization of prior service costs/(credits) | (9) | (73) | (87.6) |
| Curtailments/settlements | 41 | 11 | 262.2 |
| Other costs | 28 | 16 | 76.2 |
| Total non-operating costs/(income) | $615 | $1,572 | (60.9)% |
| Total retirement-related plans—cost | $2,072 | $3,066 | (32.4)% |
Paragraphs:
Retirement-Related Plans
The following table provides the total pre-tax cost for all retirement-related plans. Total operating costs/(income) are included in the Consolidated Income Statement within the caption (e.g., Cost, SG&A, RD&E) relating to the job function of the plan participants.
Total pre-tax retirement-related plan cost decreased by $994 million compared to 2018, primarily driven by a decrease in recognized actuarial losses ($1,123 million), primarily due to the change in the amortization period in the U.S. Qualified Personal Pension Plan and higher expected return on plan assets ($143 million), partially offset by higher interest costs ($203 million).
As discussed in the “Operating (non-GAAP) Earnings” section, we characterize certain retirement-related costs as operating and others as non-operating. Utilizing this characterization, operating retirement-related costs in 2019 were $1,457 million, a decrease of $37 million compared to 2018. Non-operating costs of $615 million in 2019 decreased $957 million year to year, driven primarily by the same factors as above.
Question:
What caused the Total pre-tax retirement-related plan cost to decrease?
Answer: driven by a decrease in recognized actuarial losses ($1,123 million), primarily due to the change in the amortization period in the U.S. Qualified Personal Pension