Retirement Benefits - Plan Asssets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value Of Retirement Plan Investments [Line Items]
Target Allocation	100.00%	100.00%
US Plans [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	$ 756.3	$ 685.4	$ 698.4
Actual Allocation	100.00%	100.00%
Target Allocation	100.00%	100.00%
US Plans [Member] | Cash, cash equivalents and receivables Member
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	3.5	3.5
Actual Allocation	1.00%	0.00%
Target Allocation	0.00%	0.00%
US Plans [Member] | Us Large Cap Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	227.3	209.9
Actual Allocation	30.00%	31.00%
Target Allocation	30.00%	30.00%
US Plans [Member] | Us Small Mid Cap Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	60.8	55.2
Actual Allocation	8.00%	8.00%
Target Allocation	8.00%	8.00%
US Plans [Member] | International Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	94.1	79.8
Actual Allocation	12.00%	12.00%
Target Allocation	12.00%	12.00%
US Plans [Member] | High Yield Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	61.9	55.2
Actual Allocation	8.00%	8.00%
Target Allocation	8.00%	8.00%
US Plans [Member] | Emerging Markets Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	30.4	27.0
Actual Allocation	4.00%	4.00%
Target Allocation	4.00%	4.00%
US Plans [Member] | Long Duration Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	179.0	158.0
Actual Allocation	24.00%	23.00%
Target Allocation	23.00%	23.00%
US Plans [Member] | Hedge fund of funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	99.3	96.8
Actual Allocation	13.00%	14.00%
Target Allocation	15.00%	15.00%
Non-US Plans [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	283.0	230.5	218.6
Actual Allocation	100.00%	100.00%
Target Allocation	100.00%	100.00%
Non-US Plans [Member] | Cash, cash equivalents and receivables Member
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	2.6	1.0
Actual Allocation	1.00%
Non-US Plans [Member] | Equity Securities [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	108.2	86.6
Actual Allocation	38.00%	38.00%
Target Allocation	39.00%	40.00%
Non-US Plans [Member] | Us Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	25.8	21.8
Non-US Plans [Member] | Canadian Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	31.7	26.5
Non-US Plans [Member] | European Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	7.4	5.3
Non-US Plans [Member] | Asia Pacific Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	1.3	1.1
Non-US Plans [Member] | Emerging Markets Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	4.7	3.2
Non-US Plans [Member] | Other Non Us Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	37.3	28.7
Non-US Plans [Member] | Fixed-income securities [Member] Member
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	156.9	132.0
Actual Allocation	55.00%	57.00%
Target Allocation	56.00%	55.00%
Non-US Plans [Member] | High Yield Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	10.2	9.9
Non-US Plans [Member] | Emerging Markets Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	5.8	5.5
Non-US Plans [Member] | Global Credit Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	34.3	28.9
Non-US Plans [Member] | Canadian Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	20.3	17.9
Non-US Plans [Member] | European Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	10.2	5.9
Non-US Plans [Member] | Long Duration Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	76.1	63.9
Non-US Plans [Member] | Other Types Of Investments [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	15.3	10.9
Actual Allocation	6.00%	5.00%
Target Allocation	5.00%	5.00%
Non-US Plans [Member] | Convertible securities [Member] Member
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	10.1	7.3
Non-US Plans [Member] | Commodity Derivatives [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	4.0	0
Non-US Plans [Member] | Other Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	1.2	3.6
UMWA Plans Postretirement Medical [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	268.7	268.0	310.2
Actual Allocation	100.00%	100.00%
UMWA Plans Postretirement Medical [Member] | Us Large Cap Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	97.2	101.8
Actual Allocation	36.00%	38.00%
Target Allocation	37.00%	37.00%
UMWA Plans Postretirement Medical [Member] | Us Small Mid Cap Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	23.7	23.5
Actual Allocation	9.00%	9.00%
Target Allocation	9.00%	9.00%
UMWA Plans Postretirement Medical [Member] | International Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	39.3	33.5
Actual Allocation	15.00%	13.00%
Target Allocation	14.00%	14.00%
UMWA Plans Postretirement Medical [Member] | Emerging Markets Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	11.7	11.2
Actual Allocation	4.00%	4.00%
Target Allocation	4.00%	4.00%
UMWA Plans Postretirement Medical [Member] | High Yield Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	23.1	22.6
Actual Allocation	9.00%	8.00%
Target Allocation	8.00%	8.00%
UMWA Plans Postretirement Medical [Member] | Multi Asset Real Return [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	32.8	35.5
Actual Allocation	12.00%	13.00%
Target Allocation	13.00%	13.00%
UMWA Plans Postretirement Medical [Member] | Hedge fund of funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	40.9	39.9
Actual Allocation	15.00%	15.00%
Target Allocation	15.00%	15.00%
Black Lung And Other Plans Postretirement [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	0	0	0
Pension plan [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	1,039.3	915.9	917.0
Retirement benefits other than pension [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	268.7	268.0	310.2
Netherlands [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	$ 142.3	$ 112.2