Postretirement Health Care and Life Insurance Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 years	Dec. 31, 2011 years	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Amortization Period	11.75
Postretirement Health Care and Life Insurance Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of actuarial gains and losses amortized	0.00%
Defined Benefit Plan, Amortization Period	11.75	11.70
Components of net periodic postretirement benefit cost
Service cost for benefits earned	$ 14.9	$ 13.9	$ 12.9
Interest cost on accumulated postretirement benefit obligation	54.9	57.9	58.2
Amortization of prior service cost	2.5	2.8	2.6
Amortization of actuarial loss	32.8	26.9	24.9
Net periodic postretirement benefit cost	105.1	101.5	98.6
Defined Benefit Plan, Amortization of Net Gains (Losses)	24.1
Defined Benefit Plan, Amortization of Net Prior Service Cost (Credit)	$ 1.7