| Schedule of Pension Plan Expense/(Income) |
he components of net periodic benefit expense/(income) for our non-contributory qualified defined benefit pension plan (Primary Pension Plan) and non-contributory supplemental pension plans were as follows: | | | | | | | | | | | | | | | | | | Three Months Ended | | Nine Months Ended | ($ in millions) | October 29,
2016 | | October 31,
2015 | | October 29,
2016 | | October 31,
2015 | Primary Pension Plan | | | | | | | | Service cost | $ | 14 |
| | $ | 17 |
| | $ | 41 |
| | $ | 52 |
| Interest cost | 38 |
| | 49 |
| | 114 |
| | 147 |
| Other cost | — |
| | 2 |
| | — |
| | 5 |
| Expected return on plan assets | (54 | ) | | (89 | ) | | (161 | ) | | (267 | ) | Amortization of prior service cost/(credit) | 2 |
| | 2 |
| | 6 |
| | 6 |
| Net periodic benefit expense/(income) | $ | — |
| | $ | (19 | ) | | $ | — |
| | $ | (57 | ) | | | | | | | | | Supplemental Pension Plans | | | | | | | | Interest cost | 1 |
| | 2 |
| | 5 |
| | 5 |
| Net periodic benefit expense/(income) | $ | 1 |
| | $ | 2 |
| | $ | 5 |
| | $ | 5 |
| | | | | | | | | Primary and Supplemental Pension Plans Total | | | | | | | | Service cost | $ | 14 |
| | $ | 17 |
| | $ | 41 |
| | $ | 52 |
| Interest cost | 39 |
| | 51 |
| | 119 |
| | 152 |
| Other cost | — |
| | 2 |
| | — |
| | 5 |
| Expected return on plan assets | (54 | ) | | (89 | ) | | (161 | ) | | (267 | ) | Amortization of prior service cost/(credit) | 2 |
| | 2 |
| | 6 |
| | 6 |
| Net periodic benefit expense/(income) | $ | 1 |
| | $ | (17 | ) | | $ | 5 |
| | $ | (52 | ) |
|