The company's traditional defined benefit plan was closed Dec. 31, 2012. Employees hired after that date are eligible to participate in a cash balance plan.

As of Dec. 31, defined benefit plan assets totaled $14.73 billion, and projected benefit obligations totaled $17.31 billion, for a funding ratio of 85.1%, up from 84.3% a year earlier. The discount rate for the plan dropped to 4.11% in 2016 from 4.37% the previous year.

The plan's target allocation is 58% fixed income, 27% global equity, 10% real assets and 5% absolute return.