Retirement Benefits - Assumptions (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net periodic pension cost (credit) [Line Items]
Discount rate - benefit obligation at year end	4.20%	4.60%	5.30%
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	4.60%	5.30%	5.90%
Expected return on assets - Pension cost	8.25%	8.75%	8.75%
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	5.40%	5.80%	6.20%
Discount rate - benefit obligation at year end	5.30%	5.40%	5.80%
Expected return on assets - Pension cost	4.92%	5.16%	5.54%
Average rate of increase in salaries - pension cost	3.20%	3.30%	3.10%
Average rate of increase in salaries - benefit obligation at year end	3.80%	3.20%	3.30%
UMWA Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	4.40%	5.30%	5.90%
Discount rate - benefit obligation at year end	3.90%	4.40%	5.30%
Black Lung And Other Plans Postretirement [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	4.20%	4.80%	5.30%
Discount rate - benefit obligation at year end	3.50%	4.20%	4.80%
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	4.40%	5.20%	5.80%
Discount rate - benefit obligation at year end	3.90%	4.40%	5.20%
Expected return on assets - Pension cost	8.50%	8.75%	8.75%