Employee Benefits (Details) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.0	$ 1.1
Interest cost	15.2	14.0
Expected return on plan assets	(13.4)	(13.9)
Amortization of net loss	3.2	3.7
Total periodic pension cost	6.0	4.9
Expected future benefit payments, remainder of the year	79.9
Contributions by employer	$ 13.8