Fair Value Accounting (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets:
Cash equivalents	$ 139.8	$ 246.6
Restricted cash	218.9	240.3
Fuel derivative instruments	0
Total assets	359.3	487.6
Interest rate hedges:
Fuel derivative instruments	0.3	0.1
Total liabilities	52.2	56.9
Equity Call Agreement [Member]
Assets:
Equity call agreement with TRIP Holdings equity investor	0.6	0.7
Interest rate hedges:
Equity put agreement with TRIP Holdings equity investor	2.2	3.1
Wholly Owned Subsidiaries [Member]
Interest rate hedges:
Interest rate hedges	44.3	48.9
TRIP Holdings [Member]
Interest rate hedges:
Interest rate hedges	5.4	4.8
Level 1 [Member]
Assets:
Cash equivalents	139.8	246.6
Restricted cash	218.9	240.3
Total assets	358.7	486.9
Level 2 [Member]
Assets:
Fuel derivative instruments	0
Total assets	0
Interest rate hedges:
Fuel derivative instruments	0.3	0.1
Total liabilities	50.0	53.8
Level 2 [Member] | Wholly Owned Subsidiaries [Member]
Interest rate hedges:
Interest rate hedges	44.3	48.9
Level 2 [Member] | TRIP Holdings [Member]
Interest rate hedges:
Interest rate hedges	5.4	4.8
Level 3 [Member]
Assets:
Total assets	0.6	0.7
Interest rate hedges:
Total liabilities	2.2	3.1
Level 3 [Member] | Equity Call Agreement [Member]
Assets:
Equity call agreement with TRIP Holdings equity investor	0.6	0.7
Interest rate hedges:
Equity put agreement with TRIP Holdings equity investor	$ 2.2	$ 3.1