Retirement Benefits - Assumptions (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement benefits other than pension
Defined Benefit Plan Disclosure [Line Items]
Pension cost	4.40%	3.70%	4.20%
Benefit obligation at year end	3.30%	4.40%	3.70%
Expected return on assets	8.00%	8.00%	8.25%
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Pension cost	4.40%	3.70%	4.30%
Benefit obligation at year end	3.30%	4.40%	3.70%
Expected return on assets	7.00%	7.25%	7.25%
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Pension cost	4.00%	3.50%	3.70%
Benefit obligation at year end	3.20%	4.00%	3.50%
Expected return on assets	5.64%	5.62%	5.50%
Average rate of increase in salaries - pension cost	2.60%	2.60%	2.70%
Average rate of increase in salaries - benefit obligation at year end	2.60%	2.60%	2.60%
UMWA Plans
Defined Benefit Plan Disclosure [Line Items]
Pension cost	4.30%	3.60%	4.10%
Benefit obligation at year end	3.20%	4.30%	3.60%
Black Lung and Other Plans
Defined Benefit Plan Disclosure [Line Items]
Pension cost	4.20%	3.50%	3.90%
Benefit obligation at year end	3.10%	4.20%	3.50%