Retirement Benefits - Plan Asssets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
US Plans [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	$ 811.8	$ 756.3	$ 685.4
Actual Allocation	100.00%	100.00%
Target Allocation	100.00%	100.00%
US Plans [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	40.0	99.3	96.8
US Plans [Member] | Cash, cash equivalents and receivables [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	3.8	3.5
Actual Allocation	0.00%	1.00%
Target Allocation	0.00%	0.00%
US Plans [Member] | Us Large Cap Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	16.00%	30.00%
Target Allocation	16.00%	30.00%
US Plans [Member] | Us Large Cap Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	132.1	227.3
US Plans [Member] | Us Small Mid Cap Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	7.00%	8.00%
Target Allocation	7.00%	8.00%
US Plans [Member] | Us Small Mid Cap Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	58.6	60.8
US Plans [Member] | International Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	14.00%	12.00%
Target Allocation	14.00%	12.00%
US Plans [Member] | International Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	114.4	94.1
US Plans [Member] | Emerging Markets Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	4.00%
Target Allocation	4.00%
US Plans [Member] | Emerging Markets Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	31.7
US Plans [Member] | Dynamic Asset Allocation [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	6.00%
Target Allocation	6.00%
US Plans [Member] | Dynamic Asset Allocation [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	50.2
US Plans [Member] | High Yield Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	3.00%	8.00%
Target Allocation	3.00%	8.00%
US Plans [Member] | High Yield Fixed Income Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	24.5	61.9
US Plans [Member] | Emerging Markets Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	3.00%	4.00%
Target Allocation	3.00%	4.00%
US Plans [Member] | Emerging Markets Fixed Income Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	23.2	30.4
US Plans [Member] | Long-duration 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	32.00%	24.00%
Target Allocation	32.00%	23.00%
US Plans [Member] | Long-duration 1 [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	190.8	139.9
US Plans [Member] | Long-duration 2 [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	65.0	39.1
US Plans [Member] | Hedge fund of funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	5.00%	13.00%
Target Allocation	5.00%	15.00%
US Plans [Member] | Hedge fund of funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	37.3	99.3
US Plans [Member] | Core Property [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	5.00%
Target Allocation	5.00%
US Plans [Member] | Core Property [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	40.2
US Plans [Member] | Structured Credit [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	5.00%
Target Allocation	5.00%
US Plans [Member] | Structured Credit [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	40.0
Non-US Plans [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	322.0	283.0	230.5
Actual Allocation	100.00%	100.00%
Target Allocation	100.00%	100.00%
Non-US Plans [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	167.9	140.1
Non-US Plans [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	154.1	142.9
Non-US Plans [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	0	0.6	0.6
Non-US Plans [Member] | Cash, cash equivalents and receivables [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	5.2	2.6
Actual Allocation	2.00%	1.00%
Non-US Plans [Member] | Equity Securities [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	127.0	108.2
Actual Allocation	39.00%	38.00%
Target Allocation	39.00%	39.00%
Non-US Plans [Member] | Us Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	30.0	25.8
Non-US Plans [Member] | Canadian Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	38.3	31.7
Non-US Plans [Member] | European Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	8.9	7.4
Non-US Plans [Member] | Asia Pacific Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	1.7	1.3
Non-US Plans [Member] | Emerging Markets Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	9.3	4.7
Non-US Plans [Member] | Other Non Us Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	38.8	37.3
Non-US Plans [Member] | Fixed-income securities [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	171.9	156.9
Actual Allocation	53.00%	55.00%
Target Allocation	55.00%	56.00%
Non-US Plans [Member] | High Yield Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	12.3	10.2
Non-US Plans [Member] | Emerging Markets Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	6.9	5.8
Non-US Plans [Member] | Global Credit Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	37.5	34.3
Non-US Plans [Member] | Canadian Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	24.8	20.3
Non-US Plans [Member] | European Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	11.0	10.2
Non-US Plans [Member] | Long-duration 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	79.4	76.1
Non-US Plans [Member] | Other Types Of Investments [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	17.9	15.3
Actual Allocation	6.00%	6.00%
Target Allocation	6.00%	5.00%
Non-US Plans [Member] | Convertible securities [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	12.0	10.1
Non-US Plans [Member] | Commodity Derivatives [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	4.7	4.0
Non-US Plans [Member] | Other Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	1.2	1.2
UMWA Plans Postretirement Medical [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	284.4	268.7	268.0
Actual Allocation	100.00%	100.00%
Target Allocation	100.00%	100.00%
UMWA Plans Postretirement Medical [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	0	40.9	39.9
UMWA Plans Postretirement Medical [Member] | Us Large Cap Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	38.00%	36.00%
Target Allocation	37.00%	37.00%
UMWA Plans Postretirement Medical [Member] | Us Large Cap Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	107.0	97.2
UMWA Plans Postretirement Medical [Member] | Us Small Mid Cap Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	10.00%	9.00%
Target Allocation	9.00%	9.00%
UMWA Plans Postretirement Medical [Member] | Us Small Mid Cap Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	27.9	23.7
UMWA Plans Postretirement Medical [Member] | International Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	15.00%	15.00%
Target Allocation	14.00%	14.00%
UMWA Plans Postretirement Medical [Member] | International Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	41.8	39.3
UMWA Plans Postretirement Medical [Member] | Emerging Markets Equity Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	4.00%	4.00%
Target Allocation	4.00%	4.00%
UMWA Plans Postretirement Medical [Member] | Emerging Markets Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	10.9	11.7
UMWA Plans Postretirement Medical [Member] | High Yield Fixed Income Funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	8.00%	9.00%
Target Allocation	8.00%	8.00%
UMWA Plans Postretirement Medical [Member] | High Yield Fixed Income Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	24.1	23.1
UMWA Plans Postretirement Medical [Member] | Multi Asset Real Return [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	10.00%	12.00%
Target Allocation	13.00%	13.00%
UMWA Plans Postretirement Medical [Member] | Multi Asset Real Return [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	29.3	32.8
UMWA Plans Postretirement Medical [Member] | Hedge fund of funds [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	10.00%	15.00%
Target Allocation	10.00%	15.00%
UMWA Plans Postretirement Medical [Member] | Hedge fund of funds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	29.2	40.9
UMWA Plans Postretirement Medical [Member] | Core Property [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Actual Allocation	5.00%
Target Allocation	5.00%
UMWA Plans Postretirement Medical [Member] | Core Property [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	14.2
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	1,133.8	1,039.3	915.9
Retirement benefits other than pension [Member]
Fair Value Of Retirement Plan Investments [Line Items]
Fair Value of Plan Assets	$ 284.4	$ 268.7	$ 268.0