Retirement Benefit Plans (Weighted Average Asset Allocations) (Details) - Pension Plans, Defined Benefit	Dec. 31, 2017	Dec. 31, 2016
Hourly Employees’ Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	0.00%	0.00%
Hourly Employees’ Pension Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	0.00%	0.00%
Hourly Employees’ Pension Plan | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	0.00%	0.00%
Hourly Employees’ Pension Plan | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	0.00%	0.00%
Hourly Employees’ Pension Plan | Other
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	0.00%	0.00%
Employees’ Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	100.00%	100.00%
Employees’ Retirement Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	55.00%	54.00%
Employees’ Retirement Plan | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	38.00%	38.00%
Employees’ Retirement Plan | Short-term investments
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	2.00%	3.00%
Employees’ Retirement Plan | Other
Defined Benefit Plan Disclosure [Line Items]
Asset allocations as a percentage of plan assets	5.00%	5.00%