Retirement Benefits - Weighted-Average Assumptions Related to Pension Plans (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase for benefit obligation	2.30%	2.20%	2.10%
Rate of compensation increase for net benefit costs	2.20%	2.10%	3.10%
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligation	0.60%	1.50%	1.10%
Discount rate for net benefit costs	1.40%	1.10%	1.00%
Expected return on plan assets for net benefit costs	4.00%	4.00%	4.40%