Retirement Plans - Plan Asset Allocation (Details)	Dec. 31, 2019	Dec. 31, 2018
U.S.
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	100.00%	100.00%
U.S. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	21.40%	21.80%
U.S. | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	69.30%	68.80%
U.S. | Alternative strategy funds
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	5.90%	7.30%
U.S. | Cash, cash equivalents and short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	3.40%	2.10%
U.K Plan
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	100.00%	100.00%
U.K Plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	17.90%	18.00%
U.K Plan | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	68.30%	71.80%
U.K Plan | Alternative strategy funds
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	13.00%	9.00%
U.K Plan | Cash, cash equivalents and short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total asset allocation	0.80%	1.20%