Retirement Benefits - Assumptions (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	5.00%	4.20%	4.60%
Discount rate - benefit obligation at year end	4.10%	5.00%	4.20%
Expected return on assets - Pension cost	8.00%	8.00%	8.25%
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	6.30%	5.30%	5.40%
Discount rate - benefit obligation at year end	5.10%	6.30%	5.30%
Expected return on assets - Pension cost	5.83%	4.64%	4.92%
Average rate of increase in salaries - pension cost	3.90%	3.80%	3.20%
Average rate of increase in salaries - benefit obligation at year end	3.90%	3.90%	3.80%
UMWA Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	4.70%	3.90%	4.40%
Discount rate - benefit obligation at year end	4.00%	4.70%	3.90%
Black Lung And Other Plans Postretirement [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	4.40%	3.50%	4.20%
Discount rate - benefit obligation at year end	3.70%	4.40%	3.50%
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	4.70%	3.90%	4.40%
Discount rate - benefit obligation at year end	4.10%	4.70%	3.90%
Expected return on assets - Pension cost	8.25%	8.25%	8.50%