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, 2012	Dec. 31, 2011
Pension Plans, Defined Benefit [Member]
Assumed health care cost trend rates used to calculate benefits expenses [Abstract]
Estimated benefits expense for next fiscal year			35.6
Estimated amortization of actuarial loss from AOCI for next fiscal year			27.5
Estimated amortization of prior service cost from AOCI for next fiscal year			1.1
Pension Plans, Defined Benefit, Qualified Only [Member]
Assumptions used to calculate pension and postretirement benefits expenses [Abstract]
Discount rate used to calculate benefits expenses (in hundredths)	5.75%	6.50%	4.80%	5.75%
Rate of increase in compensation used to calculate benefits expenses (in hundredths)	4.00%	4.00%	5.50%	4.00%
Long-term return on assets used to calculate benefits expenses (in hundredths)	7.25%	7.25%	7.25%	7.25%
Pension Plans, Defined Benefit, Nonqualified Only [Member]
Assumptions used to calculate pension and postretirement benefits expenses [Abstract]
Discount rate used to calculate benefits expenses (in hundredths)	5.75%	6.50%	3.30%	5.75%
Rate of increase in compensation used to calculate benefits expenses (in hundredths)	4.00%	4.00%	5.50%	4.00%
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%	4.40%	5.75%
Long-term return on assets used to calculate benefits expenses (in hundredths)	7.25%	7.25%	7.25%	7.25%
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%	7.00%	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	2013	2013	2014	2014
Estimated benefits expense for next fiscal year			5.0
Estimated amortization of actuarial loss from AOCI for next fiscal year			3.0
Effect of 1% increase in the health care inflation rate on the yearly service and interest cost			0
Effect of 1% increase in the health care inflation rate on the accumulated post-retirement benefit obligation			0.9
Effect of 1% decrease in the health care inflation rate on the yearly service and interest cost			0
Effect of 1% decrease in the health care inflation rate on the accumulated post-retirement benefit obligation			0.8