Retirement Benefits - Assumptions (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net periodic pension cost (credit) [Line Items]
Discount rate - benefit obligation at year end	4.60%	5.30%	5.90%
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	5.30%	5.90%	6.60%
Expected return on assets - Pension cost	8.75%	8.75%	8.75%
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	5.80%	6.20%	6.20%
Discount rate - benefit obligation at year end	5.40%	5.80%	6.20%
Expected return on assets - Pension cost	5.16%	5.54%	5.78%
Average rate of increase in salaries - pension cost	3.30%	3.10%	4.00%
Average rate of increase in salaries - benefit obligation at year end	3.20%	3.30%	3.10%
Umwa Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	5.30%	5.90%	6.20%
Discount rate - benefit obligation at year end	4.40%	5.30%	5.90%
Black Lung And Other Plans Postretirement [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	4.80%	5.30%	6.30%
Discount rate - benefit obligation at year end	4.20%	4.80%	5.40%
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Discount rate - pension cost	5.20%	5.80%	6.20%
Discount rate - benefit obligation at year end	4.40%	5.20%	5.90%
Expected return on assets - Pension cost	8.75%	8.75%	8.75%