Fair Value Measurements (Details) (Fair Value Measurements Recurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Interest rate swaps [Member]
Summary of fair value instruments
Interest rate swaps	$ (8.4)	$ (9.0)
Interest rate swaps [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Summary of fair value instruments
Interest rate swaps	0	0
Interest rate swaps [Member] | Significant Other Observable Inputs (Level 2) [Member]
Summary of fair value instruments
Interest rate swaps	(8.4)	(9.0)
Interest rate swaps [Member] | Significant Unobservable Inputs (Level 3) [Member]
Summary of fair value instruments
Interest rate swaps	0	0
Available-for-sale securities [Member]
Summary of fair value instruments
Available-for-sale securities	14.6	3.8
Available-for-sale securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Summary of fair value instruments
Available-for-sale securities	14.6	3.8
Available-for-sale securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Summary of fair value instruments
Available-for-sale securities	0	0
Available-for-sale securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Summary of fair value instruments
Available-for-sale securities	0	0
Deferred compensation plan assets [Member]
Summary of fair value instruments
Other assets, fair value disclosure	9.4	8.0
Deferred compensation plan assets [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Summary of fair value instruments
Other assets, fair value disclosure	0	0
Deferred compensation plan assets [Member] | Significant Other Observable Inputs (Level 2) [Member]
Summary of fair value instruments
Other assets, fair value disclosure	9.4	8.0
Deferred compensation plan assets [Member] | Significant Unobservable Inputs (Level 3) [Member]
Summary of fair value instruments
Other assets, fair value disclosure	0	0
Supplementary pension plan assets [Member]
Summary of fair value instruments
Other assets, fair value disclosure	8.2	7.6
Supplementary pension plan assets [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Summary of fair value instruments
Other assets, fair value disclosure	0	0
Supplementary pension plan assets [Member] | Significant Other Observable Inputs (Level 2) [Member]
Summary of fair value instruments
Other assets, fair value disclosure	8.2	7.6
Supplementary pension plan assets [Member] | Significant Unobservable Inputs (Level 3) [Member]
Summary of fair value instruments
Other assets, fair value disclosure	$ 0	$ 0