Derivative Instruments Derivative Instruments Not Designated as Hedging Instruments (Details) (Interest Rate Swap [Member], Interest Expense [Member], Derivatives not designated as hedging instruments [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Interest Rate Swap [Member] | Interest Expense [Member] | Derivatives not designated as hedging instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net periodic cash settlements and accrued interest	$ 172.0	$ 169.6	$ 201.1
Total expense for derivatives	$ 34.4	$ 140.0	$ 184.2