Retirement Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation for all defined benefit pension plans	$ 143.0	$ 126.4
Percentage of excess gains and losses over benefit obligation or market value of assets amortized	10.00%
Costs of defined contribution plans	7.8	7.0	8.8
Number of participates covering under multi employer pension plan	400
Costs of bargaining unit-sponsored multi-employer plans and defined contribution plans	1.0	0.9	0.8
Weighted average annual rate of increase in the per capita cost of covered health care benefits assumed	7.60%
Assumed decrease of weighted average health care cost trend rate	4.48%
Year that reaches assumed decrease of weighted average health care cost trend rate	2028
Increase in service and interest cost components of the net periodic benefit cost, as 1% increase in health care cost trend rates	0.2
Increase in accumulated postretirement benefit obligation, as 1% increase in health care cost trend rates	1.5
Decrease in service and interest cost components of the net periodic benefit cost, as 1% decrease in health care cost trend rates	0.1
Decrease in accumulated postretirement benefit obligation, as 1% decrease in health care cost trend rates	1.3
Target allocation of fund assets in equities, minimum	55.00%
Target allocation of fund assets in equities, maximum	75.00%
Target allocation of fund assets in equities	66.00%
Target allocation of fund assets in fixed income securities, minimum	25.00%
Target allocation of fund assets in fixed income securities, maximum	45.00%
Target allocation of fund assets in fixed income securities	34.00%
Minimum fund performance period of plan assets	3
Maximum fund performance period of plan assets	5
Future estimated benefit payments for year 2012	9.9
Future estimated benefit payments for year 2013	9.4
Future estimated benefit payments for year 2014	10.7
Future estimated benefit payments for year 2015	10.0
Future estimated benefit payments for year 2016	10.0
Future estimated benefit payments for years 2017 - 2021	55.9
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contribution for next fiscal year	9.4
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contribution for next fiscal year	0.9
Defined Contribution Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contribution for next fiscal year	$ 11.7