Employee Benefits Assumptions used to calculate net pension and postretirement benefit costs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Defined Benefit [Member]
Assumed health care cost trend rates used to calculate net benefit costs [Abstract]
Estimated net benefit cost for next fiscal year	$ 19.1
Estimated amortization of actuarial loss from AOCI for next fiscal year	15.7
Estimated amortization of prior service cost from AOCI for next fiscal year	0.6
Pension Plans, Defined Benefit, Qualified Only [Member]
Assumptions used to calculate net pension and postretirement benefit costs [Abstract]
Discount rate used to calculate net benefit costs (in hundredths)	4.20%	4.80%	5.75%
Rate of increase in compensation used to calculate net benefit costs (in hundredths)	5.50%	5.50%	4.00%
Long-term return on assets used to calculate net benefit costs (in hundredths)	7.25%	7.25%	7.25%
Pension Plans, Defined Benefit, Nonqualified Only [Member]
Assumptions used to calculate net pension and postretirement benefit costs [Abstract]
Discount rate used to calculate net benefit costs (in hundredths)	2.40%	3.30%	5.75%
Rate of increase in compensation used to calculate net benefit costs (in hundredths)	5.50%	5.50%	4.00%
Other Postretirement Benefit Plans, Defined Benefit [Member]
Assumptions used to calculate net pension and postretirement benefit costs [Abstract]
Discount rate used to calculate net benefit costs (in hundredths)	4.00%	4.40%	5.75%
Long-term return on assets used to calculate net benefit costs (in hundredths)	7.25%	7.25%	7.25%
Assumed health care cost trend rates used to calculate net benefit costs [Abstract]
Health-care inflation rate used to calculate net benefit costs (in hundredths)	8.50%	7.00%	8.00%
Ultimate health care cost trend rate used to calculate net benefit costs (in hundredths)	4.50%	5.00%	5.00%
Year that rate reaches ultimate trend rate, used to calculate net benefit costs	2021	2014	2014
Estimated net benefit cost for next fiscal year	2.8
Estimated amortization of actuarial loss from AOCI for next fiscal year	1.2
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	0.8
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	$ 0.7