Fair Value Accounting (Details) (Fair value measurements, recurring, USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Level 1
Assets:
Cash equivalents	$ 137.0		$ 246.6
Restricted cash	227.0		223.2
Total assets	364.0		469.8
Liabilities:
Total liabilities	0		0
Level 1 | Equity call agreement with TRIP Holdings equity investor
Assets:
Equity call agreement with TRIP Holdings equity investor			0	[1]
Level 1 | Fuel derivative instruments
Assets:
Fuel derivative instruments			0	[1]
Level 1 | Equity put agreement with TRIP Holdings equity investor
Liabilities:
Equity put agreement with TRIP Holdings equity investor			0	[2]
Level 1 | Wholly-owned subsidiary | Interest rate hedges
Liabilities:
Interest rate hedges	0	[3]	0	[3]
Level 1 | Partially-owned subsidiary | Interest rate hedges
Liabilities:
Interest rate hedges	0	[3]	0	[3]
Level 2
Assets:
Cash equivalents	0		155.0
Restricted cash	0		0
Total assets	0		155.1
Liabilities:
Total liabilities	31.7		42.8
Level 2 | Equity call agreement with TRIP Holdings equity investor
Assets:
Equity call agreement with TRIP Holdings equity investor			0	[1]
Level 2 | Fuel derivative instruments
Assets:
Fuel derivative instruments			0.1	[1]
Level 2 | Equity put agreement with TRIP Holdings equity investor
Liabilities:
Equity put agreement with TRIP Holdings equity investor			0	[2]
Level 2 | Wholly-owned subsidiary | Interest rate hedges
Liabilities:
Interest rate hedges	28.9	[3]	37.6	[3]
Level 2 | Partially-owned subsidiary | Interest rate hedges
Liabilities:
Interest rate hedges	2.8	[3]	5.2	[3]
Level 3
Assets:
Cash equivalents	0		0
Restricted cash	0		0
Total assets	0		0.8
Liabilities:
Total liabilities	0		2.9
Level 3 | Equity call agreement with TRIP Holdings equity investor
Assets:
Equity call agreement with TRIP Holdings equity investor			0.8	[1]
Level 3 | Fuel derivative instruments
Assets:
Fuel derivative instruments			0	[1]
Level 3 | Equity put agreement with TRIP Holdings equity investor
Liabilities:
Equity put agreement with TRIP Holdings equity investor			2.9	[2]
Level 3 | Wholly-owned subsidiary | Interest rate hedges
Liabilities:
Interest rate hedges	0	[3]	0	[3]
Level 3 | Partially-owned subsidiary | Interest rate hedges
Liabilities:
Interest rate hedges	0	[3]	0	[3]
Total
Assets:
Cash equivalents	137.0		401.6
Restricted cash	227.0		223.2
Total assets	364.0		625.7
Liabilities:
Total liabilities	31.7		45.7
Total | Equity call agreement with TRIP Holdings equity investor
Assets:
Equity call agreement with TRIP Holdings equity investor			0.8	[1]
Total | Fuel derivative instruments
Assets:
Fuel derivative instruments			0.1	[1]
Total | Equity put agreement with TRIP Holdings equity investor
Liabilities:
Equity put agreement with TRIP Holdings equity investor			2.9	[2]
Total | Wholly-owned subsidiary | Interest rate hedges
Liabilities:
Interest rate hedges	28.9	[3]	37.6	[3]
Total | Partially-owned subsidiary | Interest rate hedges
Liabilities:
Interest rate hedges	$ 2.8	[3]	$ 5.2	[3]

[1] Included in other assets on the consolidated balance sheet.

[2] Included in other liabilities on the consolidated balance sheet.

[3] Included in accrued liabilities on the consolidated balance sheet.