Financial Instruments and Risk Management (Impact of Cash Flow Hedges on Accumulated Other Comprehensive Income) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Gain (Loss) on Interest Rate Fair Value Hedge Ineffectiveness	$ 0	$ 0	$ 0
Net unamortized losses at end of year, net of taxes of $5.8 and $7.9	(13.5)
Net unamortized losses at end of year, net of taxes of $3.7 and $5.8	(11.1)	(13.5)
Treasury Locks [Member]
Net unamortized losses at end of year, net of taxes of $5.8 and $7.9	(10.7)	(14.6)
Reclassification of net losses to earnings, net of taxes of $2.1 and $2.1	3.9	3.9
Net unamortized losses at end of year, net of taxes of $3.7 and $5.8	(6.8)	(10.7)	(14.6)
Net unamortized losses at beginning of year, tax effect	3.7	5.8	7.9
Reclassification of net losses to earnings, tax effect	2.1	2.1
Net unamortized losses at end of year, tax effect	$ 3.7	$ 5.8	$ 7.9