Fair Value Accounting (Details) (Fair value measurements, recurring, USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Level 1
Assets:
Cash equivalents	$ 246.6		$ 246.6
Restricted cash	223.2		240.3
Total assets	469.8		486.9
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]	0	[1]
Level 1 | Fuel derivative instruments
Assets:
Derivative assets	0	[1]
Liabilities:
Fuel derivative instruments	0	[2]	0	[2]
Level 1 | Equity put agreement with TRIP Holdings equity investor
Liabilities:
Other Liabilities, Fair Value Disclosure	0	[3]	0	[3]
Level 1 | Wholly-owned subsidiaries | Interest rate hedges
Liabilities:
Equity put agreement with TRIP Holdings equity investor	0	[2]	0	[2]
Level 1 | TRIP Holdings | Interest rate hedges
Liabilities:
Equity put agreement with TRIP Holdings equity investor	0	[2]	0	[2]
Level 2
Assets:
Cash equivalents	155.0		0
Restricted cash	0		0
Total assets	155.1		0
Liabilities:
Total liabilities	42.8		53.8
Level 2 | Equity call agreement with TRIP Holdings equity investor
Assets:
Equity call agreement with TRIP Holdings equity investor	0	[1]	0	[1]
Level 2 | Fuel derivative instruments
Assets:
Derivative assets	0.1	[1]
Liabilities:
Fuel derivative instruments	0	[2]	0.1	[2]
Level 2 | Equity put agreement with TRIP Holdings equity investor
Liabilities:
Other Liabilities, Fair Value Disclosure	0	[3]	0	[3]
Level 2 | Wholly-owned subsidiaries | Interest rate hedges
Liabilities:
Equity put agreement with TRIP Holdings equity investor	37.6	[2]	48.9	[2]
Level 2 | TRIP Holdings | Interest rate hedges
Liabilities:
Equity put agreement with TRIP Holdings equity investor	5.2	[2]	4.8	[2]
Level 3
Assets:
Cash equivalents	0		0
Restricted cash	0		0
Total assets	0.8		0.7
Liabilities:
Total liabilities	2.9		3.1
Level 3 | Equity call agreement with TRIP Holdings equity investor
Assets:
Equity call agreement with TRIP Holdings equity investor	0.8	[1]	0.7	[1]
Level 3 | Fuel derivative instruments
Assets:
Derivative assets	0	[1]
Liabilities:
Fuel derivative instruments	0	[2]	0	[2]
Level 3 | Equity put agreement with TRIP Holdings equity investor
Liabilities:
Other Liabilities, Fair Value Disclosure	2.9	[3]	3.1	[3]
Level 3 | Wholly-owned subsidiaries | Interest rate hedges
Liabilities:
Equity put agreement with TRIP Holdings equity investor	0	[2]	0	[2]
Level 3 | TRIP Holdings | Interest rate hedges
Liabilities:
Equity put agreement with TRIP Holdings equity investor	0	[2]	0	[2]
Total
Assets:
Cash equivalents	401.6		246.6
Restricted cash	223.2		240.3
Total assets	625.7		487.6
Liabilities:
Total liabilities	45.7		56.9
Total | Equity call agreement with TRIP Holdings equity investor
Assets:
Equity call agreement with TRIP Holdings equity investor	0.8	[1]	0.7	[1]
Total | Fuel derivative instruments
Assets:
Derivative assets	0.1	[1]
Liabilities:
Fuel derivative instruments	0	[2]	0.1	[2]
Total | Equity put agreement with TRIP Holdings equity investor
Liabilities:
Other Liabilities, Fair Value Disclosure	2.9	[3]	3.1	[3]
Total | Wholly-owned subsidiaries | Interest rate hedges
Liabilities:
Equity put agreement with TRIP Holdings equity investor	37.6	[2]	48.9	[2]
Total | TRIP Holdings | Interest rate hedges
Liabilities:
Equity put agreement with TRIP Holdings equity investor	$ 5.2	[2]	$ 4.8	[2]

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

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

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