Other Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other assets
Other assets	$ 259.3	$ 128.4
Write-off of unamortized deferred financing fees	5.4	5.9	7.6
Deferred financing costs
Other assets
Other assets	219.9	92.5
Capitalized costs during period	150.0	92.1	6.3
Amortization expense for period	17.4	7.8	7.1
Deferred tax asset, long-term portion
Other assets
Other assets	18.6	24.5
Other assets
Other assets
Other assets	$ 20.8	$ 11.4