Retirement Benefits - Assumptions (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
UMWA Plans
Defined Benefit Plan Disclosure [Line Items]
Postretirement cost:	4.00%	4.70%	3.90%
Benefit obligation at year end:	4.40%	4.00%	4.70%
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Postretirement cost:	4.10%	5.00%	4.20%
Benefit obligation at year end:	4.50%	4.10%	5.00%
Expected return on assets	7.50%	8.00%	8.00%
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Postretirement cost:	5.10%	6.30%	5.30%
Benefit obligation at year end:	5.10%	5.10%	6.30%
Expected return on assets	5.58%	5.83%	4.64%
Average rate of increase in salaries - pension cost	3.90%	3.90%	3.80%
Average rate of increase in salaries - benefit obligation at year end	3.80%	3.90%	3.90%
Black Lung and Other Plans
Defined Benefit Plan Disclosure [Line Items]
Postretirement cost:	3.70%	4.40%	3.50%
Benefit obligation at year end:	4.20%	3.70%	4.40%
Retirement benefits other than pension
Defined Benefit Plan Disclosure [Line Items]
Postretirement cost:	4.10%	4.70%	3.90%
Benefit obligation at year end:	4.40%	4.10%	4.70%
Expected return on assets	8.25%	8.25%	8.25%