The following table summarizes the components of net periodic benefit cost for the Company's pension, postretirement and supplemental retirement plans for the three months ended September 30,: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Defined Benefit Pension Plans | Postretirement Benefit Plan | | Supplemental Retirement Plans | (Dollars in millions) | Three Months Ended September 30, 2021 | | Three Months Ended September 30, 2020 | | Three Months Ended September 30, 2021 | | Three Months Ended September 30, 2020 | | Three Months Ended September 30, 2021 | | Three Months Ended September 30, 2020 | Service cost | $ | — | | | $ | — | | | $ | — | | | $ | — | | | $ | — | | | $ | — | | Interest cost | 1 | | | 2 | | | — | | | — | | | — | | | — | | Less Expected return on plan assets | (2) | | | (2) | | | — | | | — | | | — | | | — | | Amortization of net actuarial loss (gain) | — | | | 1 | | | — | | | — | | | — | | | — | | Amortization of prior service cost | — | | | — | | | — | | | — | | | — | | | — | | Settlement expense (income) | — | | | 4 | | | — | | | — | | | — | | | — | | Net periodic benefit cost | $ | (1) | | | $ | 5 | | | $ | — | | | $ | — | | | $ | — | | | $ | — | |
The following table summarizes the components of net periodic benefit cost for the Company's pension, postretirement and supplemental retirement plans for the nine months ended September 30,: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Defined Benefit Pension Plans | Postretirement Benefit Plan | | Supplemental Retirement Plans | (Dollars in millions) | Nine Months Ended September 30, 2021 | | Nine Months Ended September 30, 2020 | | Nine Months Ended September 30, 2021 | | Nine Months Ended September 30, 2020 | | Nine Months Ended September 30, 2021 | | Nine Months Ended September 30, 2020 | Service cost | $ | — | | | $ | — | | | $ | — | | | $ | — | | | $ | — | | | $ | — | | Interest cost | $ | 4 | | | $ | 5 | | | — | | | — | | | — | | | — | | Less Expected return on plan assets | $ | (6) | | | $ | (6) | | | — | | | — | | | — | | | — | | Amortization of net actuarial loss (gain) | $ | 1 | | | $ | 2 | | | (1) | | | — | | | — | | | — | | Amortization of prior service cost | $ | — | | | $ | — | | | — | | | — | | | — | | | — | | Settlement expense (income) | $ | — | | | $ | 4 | | | — | | | — | | | — | | | — | | Net periodic benefit cost | $ | (1) | | | $ | 5 | | | $ | (1) | | | $ | — | | | $ | — | | | $ | — | |
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