Fair Value Measurement (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 Senior Notes [Member]	Sep. 30, 2013 Debentures With Put Feature [Member]	Sep. 30, 2013 Recurring fair value measurements [Member]	Dec. 31, 2012 Recurring fair value measurements [Member]	Sep. 30, 2013 Recurring fair value measurements [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2012 Recurring fair value measurements [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Sep. 30, 2013 Recurring fair value measurements [Member] Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2012 Recurring fair value measurements [Member] Significant Other Observable Inputs (Level 2) [Member]	Sep. 30, 2013 Recurring fair value measurements [Member] Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2012 Recurring fair value measurements [Member] Significant Unobservable Inputs (Level 3) [Member]	Sep. 30, 2013 Financial Instruments not carried at fair value [Member]	Dec. 31, 2012 Financial Instruments not carried at fair value [Member]	Sep. 30, 2013 Financial Instruments not carried at fair value [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Dec. 31, 2012 Financial Instruments not carried at fair value [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]	Sep. 30, 2013 Financial Instruments not carried at fair value [Member] Significant Other Observable Inputs (Level 2) [Member]	Dec. 31, 2012 Financial Instruments not carried at fair value [Member] Significant Other Observable Inputs (Level 2) [Member]	Sep. 30, 2013 Financial Instruments not carried at fair value [Member] Significant Unobservable Inputs (Level 3) [Member]	Dec. 31, 2012 Financial Instruments not carried at fair value [Member] Significant Unobservable Inputs (Level 3) [Member]
Assets, fair value measurements [Abstract]
Marketable securities			$ 20.1	$ 16.7	$ 20.1	$ 16.7	$ 0	$ 0	$ 0	$ 0
Derivative instruments			12.0	4.7	0	0	12.0	4.7	0	0
Total assets, fair value measurements			32.1	21.4	20.1	16.7	12.0	4.7	0	0
Liabilities, fair value measurements [Abstract]
Derivative instruments			11.3	11.7	0	0	11.3	11.7	0	0
Total liability, fair value measurements			11.3	11.7	0	0	11.3	11.7	0	0
Total debt											3,778.1	3,663.1	0	0	3,778.1	3,663.1	0	0
Total financial instruments not carried at fair value											$ 3,778.1	$ 3,663.1	$ 0	$ 0	$ 3,778.1	$ 3,663.1	$ 0	$ 0
Debt instrument, maturity date range, start		Jan. 01, 2027
Debt instrument, maturity date range, end	Dec. 31, 2043	Dec. 31, 2028