v2.4.0.6
Equity method investments (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Operating results    
Project revenue $ 52.6 $ 53.3
Project expenses 43.3 45.5
Project other expenses (2.1) (4.9)
Project income 7.2 2.9
Chambers
    
Operating results    
Project revenue 13.2 13.2
Project expenses 9.6 9.8
Project other expenses (0.6) (1.2)
Project income 3.0 2.2
Other
    
Operating results    
Project revenue 39.4 40.1
Project expenses 33.7 35.7
Project other expenses (1.5) (3.7)
Project income $ 4.2 $ 0.7