Employee Benefit Plans Measurement Assumptions (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension Plan | UNITED STATES
Defined Benefit Plans and Other Postretirement Benefit Plans
Discount Rate Assumptions Used Calculating Benefit Obligation	2.90%	3.60%
Discount Rate Assumptions Used Calculating Net Periodic Benefit Cost	3.60%	4.40%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	7.00%	7.00%
Pension Plan | UNITED KINGDOM
Defined Benefit Plans and Other Postretirement Benefit Plans
Discount Rate Assumptions Used Calculating Benefit Obligation	1.40%	2.00%
Rate of Compensation Increase Assumptions Used Calculating Benefit Obligation	2.80%	2.90%
Discount Rate Assumptions Used Calculating Net Periodic Benefit Cost	2.00%	2.90%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	4.10%	4.30%
Rate of Compensation Increase Assumptions Used Calculating Net Periodic Benefit Cost	2.90%	3.70%
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Discount Rate Assumptions Used Calculating Benefit Obligation	2.60%	3.40%
Discount Rate Assumptions Used Calculating Net Periodic Benefit Cost	3.40%	4.40%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	5.75%	5.75%