Retirement Benefits - Schedule of Health Care Cost Trend Rates (Details) - Other postretirement benefit plans |
Dec. 31, 2018 |
|---|---|
| Pre-65 | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Initial Cost Trend Rate | 6.50% |
| Ultimate Cost Trend Rate | 4.50% |
| Post-65 medical | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Initial Cost Trend Rate | 5.00% |
| Ultimate Cost Trend Rate | 4.50% |
| Post-65 prescription | |
| Defined Benefit Plan Disclosure [Line Items] | |
| Initial Cost Trend Rate | 8.00% |
| Ultimate Cost Trend Rate | 4.50% |