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, 2011	Dec. 31, 2010	Dec. 31, 2009
Net derivative losses at beginning of year, net of taxes of $7.9 and $10.1	$ (14.6)
Net derivative losses at end of year, net of taxes of $5.8 and $7.9	(13.5)	(14.6)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Effect	2.1	2.2	4.7
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Effect	2.1	2.2	4.7
Treasury Locks [Member]
Net derivative losses at beginning of year, net of taxes of $7.9 and $10.1	(14.6)	(18.8)
Reclassification of net gains to earnings, net of taxes of $2.1 and $2.2	3.9	4.2
Net derivative losses at end of year, net of taxes of $5.8 and $7.9	(10.7)	(14.6)	(18.8)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Effect	5.8	7.9	10.1
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Tax	2.1	2.2
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax Effect	$ 5.8	$ 7.9	$ 10.1