Pension Benefits | Medical and Life Benefits | |||||||||||
$ in millions | 2013 | 2012 | 2013 | 2012 | ||||||||
Change in projected benefit obligation | ||||||||||||
Projected benefit obligation at beginning of year | $27,746 | $24,129 | $2,448 | $2,235 | ||||||||
Service cost | 516 | 522 | 36 | 34 | ||||||||
Interest cost | 1,117 | 1,184 | 96 | 109 | ||||||||
Participant contributions | 12 | 12 | 77 | 81 | ||||||||
Plan amendments | — | (1 | ) | — | — | |||||||
Actuarial (gain) loss | (2,063 | ) | 3,114 | (219 | ) | 202 | ||||||
Benefits paid | (1,365 | ) | (1,220 | ) | (227 | ) | (227 | ) | ||||
Other | 9 | 6 | 13 | 14 | ||||||||
Projected benefit obligation at end of year | $25,972 | $27,746 | $2,224 | $2,448 | ||||||||