The components of net periodic benefit cost (credit) for the Corporation's qualified pension plan, non-qualified pension plan and postretirement benefit plan are as follows. | | | | | | | | | Qualified Defined Benefit Pension Plan | Three Months Ended March 31, | (in millions) | 2018 | | 2017 | Service cost | $ | 7 |
| | $ | 7 |
| | | | | Other components of net benefit credit: | | | | Interest cost | 19 |
| | 20 |
| Expected return on plan assets | (41 | ) | | (40 | ) | Amortization of prior service credit | (5 | ) | | (5 | ) | Amortization of net loss | 13 |
| | 11 |
| Total other components of net benefit credit | (14 | ) | | (14 | ) | Net periodic defined benefit credit | $ | (7 | ) | | $ | (7 | ) |
| | | | | | | | | Non-Qualified Defined Benefit Pension Plan | Three Months Ended March 31, | (in millions) | 2018 | | 2017 | Service cost | $ | — |
| | $ | 1 |
| | | | | Other components of net benefit cost: | | | | Interest cost | 2 |
| | 2 |
| Amortization of prior service credit | (2 | ) | | (2 | ) | Amortization of net loss | 2 |
| | 2 |
| Total other components of net benefit cost | 2 |
| | 2 |
| Net periodic defined benefit cost | $ | 2 |
| | $ | 3 |
|
| | | | | | | | | Postretirement Benefit Plan | Three Months Ended March 31, | (in millions) | 2018 | | 2017 | Other components of net benefit cost: | | | | Interest cost | $ | 1 |
| | $ | 1 |
| Expected return on plan assets | (1 | ) | | (1 | ) | Net periodic defined benefit cost | $ | — |
| | $ | — |
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