Employee Benefits Assumptions used to calculate pension and postretirement benefits expenses (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		12 Months Ended
	Dec. 31, 2010	Jun. 30, 2010	Dec. 31, 2011	Dec. 31, 2009	Dec. 31, 2008
Assumed health care cost trend rates used to calculate benefits expenses [Abstract]
Effect of 1% increase in the health care inflation rate on the yearly service and interest cost			$ 0.1
Effect of 1% increase in the health care inflation rate on the accumulated post-retirement benefit obligation			1.0
Effect of 1% decrease in the health care inflation rate on the yearly service and interest cost			(0.1)
Effect of 1% decrease in the health care inflation rate on the accumulated post-retirement benefit obligation			(0.9)
Pension Plans, Defined Benefit [Member]
Assumptions used to calculate pension and postretirement benefits expenses [Abstract]
Discount rate used to calculate benefits expenses (in hundredths)	5.75%	6.50%	5.75%	6.50%
Rate of increase in compensation used to calculate benefits expenses (in hundredths)	4.00%	4.00%	4.00%	4.00%
Long-term return on assets used to calculate benefits expenses (in hundredths)	7.25%	7.25%	7.25%	7.50%
Assumed health care cost trend rates used to calculate benefits expenses [Abstract]
Estimated benefits expense for next fiscal year			36.1
Estimated amortization of actuarial loss from AOCI for next fiscal year			21.4
Estimated amortization of prior service cost from AOCI for next fiscal year			1.1
Other Postretirement Benefit Plans, Defined Benefit [Member]
Assumptions used to calculate pension and postretirement benefits expenses [Abstract]
Discount rate used to calculate benefits expenses (in hundredths)	5.75%	6.50%	5.75%	6.50%
Long-term return on assets used to calculate benefits expenses (in hundredths)	7.25%	7.25%	7.25%	7.50%
Assumed health care cost trend rates used to calculate benefits expenses [Abstract]
Health-care inflation rate used to calculate benefits expenses (in hundredths)	8.00%	8.00%	8.00%	8.00%
Ultimate health care cost trend rate used to calculate benefits expenses (in hundredths)	5.00%	5.00%	5.00%	5.00%
Year that rate reaches ultimate trend rate, used to calculate benefits expenses	2014	2013		2013	2011
Estimated benefits expense for next fiscal year			6.0
Estimated amortization of actuarial loss from AOCI for next fiscal year			2.2
Estimated amortization of net transition obligation from AOCI for next fiscal year			$ 1.6