Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Significant Accounting Policies
Gross amount of port costs included in passenger ticket revenues	$ 141.7	$ 137.7	$ 268.8	$ 261.8
Balance sheet reclass from Property, plant and equipment to Other assets
Significant Accounting Policies
Prior Period Reclassification Adjustment					$ 41.9
Cash flows reclass from Other, net to Net deferred income tax (benefit) expense
Significant Accounting Policies
Prior Period Reclassification Adjustment				$ 2.9