Fair Value Measurements and Derivative Instruments (Credit Features) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			12 Months Ended
	Dec. 31, 2013 Maturity of at least five years Lower Limit	Dec. 31, 2013 Interest rate contracts derivative	Dec. 31, 2012 Interest rate contracts	Dec. 31, 2013 Standard & Poor's, BBB- Rating Lower Limit	Dec. 31, 2013 Standard & Poor's, BB Rating	Dec. 31, 2013 Moody's, Ba1 Rating	Dec. 31, 2013 Moody's, Baa3 Rating
Derivative instruments disclosure
Credit ratings for senior debt				BBB-	BB	Ba1	Baa3
Number of derivative instruments		5
Interest rate instrument term	5 years
Aggregate fair value of all derivative instruments with credit-related contingent features in net liability positions		$ 66.9	$ 55.5