Retirement Plans - Plan Asset Investment Allocation Percentage (Details) - Pension Plan	Dec. 31, 2019	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	19.00%	3.00%
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	30.00%	28.00%
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	51.00%	69.00%
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%