Retirement Benefits - Estimated Future Pension Benef Pmts (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Estimated Future Benefit Payments from Plan Assets to Beneficiaries
2013	$ 40.0
2014	39.8
2015	39.7
2016	39.2
2017	38.5
2018 through 2022	185.8
US Plans [Member]
Estimated Future Benefit Payments from Plan Assets to Beneficiaries
2013	45.5
2014	46.8
2015	48.1
2016	49.2
2017	50.8
2018 through 2022	280.5
Non-US Plans [Member]
Estimated Future Benefit Payments from Plan Assets to Beneficiaries
2013	15.6
2014	14.3
2015	15.0
2016	16.0
2017	18.1
2018 through 2022	117.6
UMWA Plans Postretirement Medical [Member]
Estimated Future Benefit Payments from Plan Assets to Beneficiaries
2013	38.1
2014	38.3
2015	38.6
2016	38.3
2017	38.0
2018 through 2022	186.8
Pension plan [Member]
Estimated Future Benefit Payments from Plan Assets to Beneficiaries
2013	61.1
2014	61.1
2015	63.1
2016	65.2
2017	68.9
2018 through 2022	398.1
Retirement benefits other than pension [Member]
Estimated Future Benefit Payments from Plan Assets to Beneficiaries
2013	43.3
2014	43.2
2015	43.2
2016	42.7
2017	42.1
2018 through 2022	203.8
Black Lung And Other Plans Postretirement [Member]
Estimated Future Benefit Payments from Plan Assets to Beneficiaries
2013	5.2
2014	4.9
2015	4.6
2016	4.4
2017	4.1
2018 through 2022	$ 17.0