Employee Benefits (Details) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.1	$ 0.9	$ 3.2	$ 2.8
Interest cost	14.0	14.8	42.1	44.5
Expected return on plan assets	(13.9)	(14.9)	(41.7)	(38.1)
Amortization of net loss	3.7	1.0	11.1	6.8
Total periodic pension cost	4.9	1.8	14.7	16.0
Expected future benefit payments, remainder of the year	62.6		62.6
Contributions by employer			$ 48.9