Employee Benefit Plans (Information for Pension Plans with a Projected and Accumulated Benefit Obligation in Excess of Plan Assets) (Details) - USD ($) $ in Millions |
Dec. 31, 2017 |
Dec. 31, 2016 |
|---|---|---|
| Defined Benefit Plan, Plan with Benefit Obligation in Excess of Plan Assets [Abstract] | ||
| Projected benefit obligation | $ 2,875 | $ 2,638 |
| Fair value of plan assets | 47 | 44 |
| Information On Pension Plans With Accumulated Benefit Obligation In Excess Of Plan Assets [Abstract] | ||
| Accumulated benefit obligation | 2,655 | 2,426 |
| Fair value of plan assets | $ 0 | $ 4 |