Fair Value Accounting (Details 1) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Interest rate hedges
Wholly-owned subsidiary	$ 45.7	$ 45.7
TRIP Holdings	47.0	48.3
Total liabilities	92.7	94.0
Fair Value, Inputs, Level 1 [Member]
Interest rate hedges
Wholly-owned subsidiary	0	0
TRIP Holdings	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 2 [Member]
Interest rate hedges
Wholly-owned subsidiary	45.7	45.7
TRIP Holdings	47.0	48.3
Total liabilities	92.7	94.0
Fair Value, Inputs, Level 3 [Member]
Interest rate hedges
Wholly-owned subsidiary	0	0
TRIP Holdings	0	0
Total liabilities	$ 0	$ 0