Fair Value Measurement (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013 Senior Notes [Member]	Jun. 30, 2013 Debentures With Put Feature [Member]	Jun. 30, 2013 Recurring fair value measurements [Member]	Dec. 31, 2012 Recurring fair value measurements [Member]	Jun. 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]	Jun. 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]	Jun. 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]	Jun. 30, 2013 Financial Instruments not carried at fair value [Member]	Dec. 31, 2012 Financial Instruments not carried at fair value [Member]	Jun. 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]	Jun. 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]	Jun. 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			$ 17.2	$ 16.7	$ 17.2	$ 16.7	$ 0	$ 0	$ 0	$ 0
Derivative instruments			5.1	4.7	0	0	5.1	4.7	0	0
Total assets, fair value measurements			22.3	21.4	17.2	16.7	5.1	4.7	0	0
Liabilities, fair value measurements [Abstract]
Derivative instruments			39.0	11.7	0	0	39.0	11.7	0	0
Total liability, fair value measurements			39.0	11.7	0	0	39.0	11.7	0	0
Total debt											5,037.2	3,663.1	0	0	5,037.2	3,663.1	0	0
Total financial instruments not carried at fair value											$ 5,037.2	$ 3,663.1	$ 0	$ 0	$ 5,037.2	$ 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