Significant Accounting Policies (Gain on Asset Dispositions) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Significant Acquisitions and Disposals [Line Items]
Disposition gains	$ 60.0	$ 42.7	$ 40.4
Residual sharing income	10.8	22.6	5.2
Non-remarketing disposition gains	20.7	19.2	27.0
Asset impairments	(5.9)	(5.0)	(6.8)
Net Gain on Asset Dispositions	$ 85.6	$ 79.5	$ 65.8