Employee Benefits Employee Benefits (Details) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.0	$ 0.9	$ 1.9	$ 1.8
Interest cost	14.8	15.3	29.7	30.6
Expected return on plan assets	(11.6)	(10.7)	(23.2)	(21.5)
Amortization of net loss	2.9	2.4	5.8	4.8
Total periodic pension cost	7.1	7.9	14.2	15.7
Defined Benefit Plan, Expected Future Benefit Payments, Remainder of Fiscal Year	76.6		76.6
Defined Benefit Plan, Contributions by Employer			$ 20.8