Retirement Benefits Plans (Narrative) (Details) - USD ($) $ in Millions |
12 Months Ended | |||
|---|---|---|---|---|
Jan. 01, 2011 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Company's pretax income and the aggregate compensation levels of participating employees | $ 6.5 | $ 6.4 | $ 5.6 | |
| Postretirement benefit plans | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Years of service, less than | 10 years | |||
| Health care cost trend assumption increased health care cost trend rates (as a percent) | 6.50% | 6.50% | ||
| Health care cost trend assumption increased health care cost trend rates (as a percent) | 5.00% | |||