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Retirement Benefits - Changes in Level 3 Investments (Details) (USD $) In Millions, unless otherwise specified				12 Months Ended					12 Months Ended					12 Months Ended
	Dec. 31, 2011 US Plans [Member]	Dec. 31, 2010 US Plans [Member]	Dec. 31, 2009 US Plans [Member]	Dec. 31, 2011 US Plans [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2010 US Plans [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Non-US Plans [Member]	Dec. 31, 2010 Non-US Plans [Member]	Dec. 31, 2009 Non-US Plans [Member]	Dec. 31, 2011 Non-US Plans [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2010 Non-US Plans [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Umwa Plans Postretirement Medical [Member]	Dec. 31, 2010 Umwa Plans Postretirement Medical [Member]	Dec. 31, 2009 Umwa Plans Postretirement Medical [Member]	Dec. 31, 2011 Umwa Plans Postretirement Medical [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2010 Umwa Plans Postretirement Medical [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Black Lung And Other Plans Postretirement [Member]	Dec. 31, 2010 Black Lung And Other Plans Postretirement [Member]	Dec. 31, 2009 Black Lung And Other Plans Postretirement [Member]	Dec. 31, 2011 Pension plan [Member]	Dec. 31, 2010 Pension plan [Member]	Dec. 31, 2009 Pension plan [Member]	Dec. 31, 2011 Retirement benefits other than pension [Member]	Dec. 31, 2010 Retirement benefits other than pension [Member]	Dec. 31, 2009 Retirement benefits other than pension [Member]
Changes in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 685.4	$ 698.4	$ 658.2	$ 98.1	$ 87.3	$ 230.5	$ 218.6	$ 188.9	$ 0.8	$ 1.5	$ 268.0	$ 310.2	$ 308.0	$ 40.4	$ 40.0	$ 0	$ 0	$ 0	$ 915.9	$ 917.0	$ 847.1	$ 268.0	$ 310.2	$ 308.0
Return on assets - relating to assets still held at the reporting date				(1.3)	1.3				0	(0.4)				(0.5)	0.4
Return on assets - relating to assets sold during the period				0					(0.2)					0
Purchases, sales and settlements					9.5					(0.3)					0
Fair value of plan assets at end of year	$ 685.4	$ 698.4	$ 658.2	$ 96.8	$ 98.1	$ 230.5	$ 218.6	$ 188.9	$ 0.6	$ 0.8	$ 268.0	$ 310.2	$ 308.0	$ 39.9	$ 40.4	$ 0	$ 0	$ 0	$ 915.9	$ 917.0	$ 847.1	$ 268.0	$ 310.2	$ 308.0

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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