Retirement Benefits - Estimated Future Pension Benef Pmts (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Net periodic pension cost (credit) [Line Items]
2013	$ 43.3
2014	42.9
2015	42.7
2016	41.9
2017 through 2021	194.3
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
2012	55.6
2013	46.1
2014	46.0
2015	47.2
2016	48.7
2017 through 2021	272.7
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
2012	18.7
2013	11.1
2014	12.8
2015	12.0
2016	13.4
2017 through 2021	85.6
Umwa Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
2013	40.9
2014	40.9
2015	41.0
2016	40.5
2017 through 2021	191.9
Pension plan [Member]
Net periodic pension cost (credit) [Line Items]
2012	74.3
2013	57.2
2014	58.8
2015	59.2
2016	62.1
2017 through 2021	358.3
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
2013	46.7
2014	46.4
2015	46.2
2016	45.5
2017 through 2021	212.6
Black Lung And Other Plans Postretirement [Member]
Net periodic pension cost (credit) [Line Items]
2013	5.8
2014	5.5
2015	5.2
2016	5.0
2017 through 2021	$ 20.7