Pension and Postretirement Benefit Plans - Narrative (Details) - Funded $ in Millions |
6 Months Ended |
|---|---|
|
Jun. 30, 2018
USD ($)
| |
| Qualified and Non-qualified Pension Benefits | |
| Benefit Plan Information | |
| Company contributions year to date | $ 259 |
| Qualified and Non-qualified Pension Benefits | Maximum | |
| Benefit Plan Information | |
| Estimated pension and postretirement employer contributions in current fiscal year | 500 |
| Qualified and Non-qualified Pension Benefits | Minimum | |
| Benefit Plan Information | |
| Estimated pension and postretirement employer contributions in current fiscal year | 300 |
| Postretirement Benefits | |
| Benefit Plan Information | |
| Company contributions year to date | $ 2 |