Employee Benefit Plans (Pension Plans with Projected Benefit Obligations in Excess of Fair Value of Plan Assets) (Details) - Pension Plans - USD ($) $ in Millions |
Dec. 31, 2017 |
Dec. 31, 2016 |
---|---|---|
Pension Plans with Benefit Obligations in Excess of the Fair Value of Plan Assets | ||
Projected benefit obligation | $ 3,676 | $ 566 |
Accumulated benefit obligation | 3,663 | 552 |
Fair value of plan assets | 3,091 | 56 |
Accumulated benefit obligation | $ 3,953 | $ 3,696 |