Employee Benefits (Details) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.1	$ 1.0
Interest cost	14.0	14.8
Expected return on plan assets	(13.9)	(11.6)
Amortization of net loss	3.7	2.9
Total periodic pension cost	4.9	7.1
Defined Benefit Plan, Expected Future Benefit Payments, Remainder of Fiscal Year	62.6
Defined Benefit Plan, Contributions by Employer	$ 12.2