Employee Benefit Plans (Amounts Included in Accumulated Other Comprehensive Income Expected to be Recognized as Components of Net Periodic Benefit Cost in Subsequent Year) (Details) $ in Millions |
Dec. 31, 2017
USD ($)
|
|---|---|
| Pension Benefits | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Amortization of prior service cost | $ (4) |
| Amortization of actuarial (gain) loss, net | 214 |
| Total | 210 |
| Other Postretirement Benefits | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Amortization of prior service cost | 1 |
| Amortization of actuarial (gain) loss, net | 17 |
| Total | $ 18 |