Retirement Benefits - Health Care Cost Trends and OPEB Future Ben Pmts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]
Effects of 1% increase on service and interest cost	$ 2.5
Effects of 1% increase on APBO	60.1
Effects of 1% decrease on service and interest cost	(2.1)
Effects of 1% decrease on APBO	(51.1)
Estimated Future Benefits Payments [Line Items]
2012	44.1
2013	43.3
2014	42.9
2015	42.7
2016	41.9
2017 through 2021	194.3
2012 Medicare Subsidy	(3.3)
2013 edicare Subsidy	(3.4)
2014 Medicare Subsidy	(3.5)
2015 Medicare Subsidy	(3.5)
2016 Medicare Subsidy	(3.6)
2017 through 2021 Medicare Subsidy	(18.3)
US Plans [Member]
Estimated Future Benefits Payments [Line Items]
2013	46.1
2014	46.0
2015	47.2
2016	48.7
2017 through 2021	272.7
Non-US Plans [Member]
Estimated Future Benefits Payments [Line Items]
2013	11.1
2014	12.8
2015	12.0
2016	13.4
2017 through 2021	85.6
UMWA plans [Member]
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Assumed health care cost trend rate used to compute current APBO for next year	7.00%	7.00%
Ultimate Health Care Cost Trend Rate	5.00%	5.00%
Estimated Future Benefits Payments [Line Items]
2012	40.2
2013	40.9
2014	40.9
2015	41.0
2016	40.5
2017 through 2021	191.9
Black lung and other plans - postretirement medical [Member]
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Assumed health care cost trend rate used to compute current APBO for next year		5.00%
Estimated Future Benefits Payments [Line Items]
2012	7.2
2013	5.8
2014	5.5
2015	5.2
2016	5.0
2017 through 2021	20.7
Pension plan [Member]
Estimated Future Benefits Payments [Line Items]
2013	57.2
2014	58.8
2015	59.2
2016	62.1
2017 through 2021	358.3
Retirement benefits other than pension [Member]
Estimated Future Benefits Payments [Line Items]
2012	47.4
2013	46.7
2014	46.4
2015	46.2
2016	45.5
2017 through 2021	$ 212.6