Goodwill and Other Intangible Assets (Goodwill and Intangible Assets Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Roll Forward]
Beginning balance	$ 24.1	$ 23.8
Acquisitions of businesses	7.6	0.3
Ending balance	31.7	24.1	$ 23.8
Finite-lived Intangible Assets [Roll Forward]
Beginning balance	31.3	38.7
Finite-Lived and Indefinite-Lived Intangibles Acquired	1.1	2.8
Amortization, including foreign currency translation	(12.5)	(10.6)	(8.3)
Ending balance	24.2	31.3	38.7
LowFares.com [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived and Indefinite-Lived Intangibles Acquired	3.9
Star & Shield LLC [Member]
Finite-lived Intangible Assets [Roll Forward]
Beginning balance	$ 0.4	0.8
Ending balance		$ 0.4	$ 0.8