Retirement Plans (Plan Asset Investment Allocation Percentage) (Details) - Pension Plan	Dec. 31, 2018	Dec. 31, 2017
United States
Asset Category
Percentage of Plan assets	100.00%	100.00%
United States | Cash and cash equivalents
Asset Category
Percentage of Plan assets	3.00%	2.00%
United States | Cash and cash equivalents | Minimum
Asset Category
Target percentage of plan assets	0.00%
United States | Cash and cash equivalents | Maximum
Asset Category
Target percentage of plan assets	10.00%
United States | Total fixed income
Asset Category
Percentage of Plan assets	28.00%	32.00%
United States | Total fixed income | Minimum
Asset Category
Target percentage of plan assets	25.00%
United States | Total fixed income | Maximum
Asset Category
Target percentage of plan assets	50.00%
United States | Total mutual funds and equities
Asset Category
Percentage of Plan assets	69.00%	66.00%
United States | Total mutual funds and equities | Minimum
Asset Category
Target percentage of plan assets	50.00%
United States | Total mutual funds and equities | Maximum
Asset Category
Target percentage of plan assets	70.00%
United Kingdom | Cash and cash equivalents | Maximum
Asset Category
Target percentage of plan assets		100.00%
United Kingdom | Equity securities | Maximum
Asset Category
Target percentage of plan assets		100.00%
United Kingdom | Commercial property | Maximum
Asset Category
Target percentage of plan assets		50.00%
United Kingdom | U.K. Government securities | Maximum
Asset Category
Target percentage of plan assets		50.00%