v2.4.0.8
Equity method investments (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Operating results        
Project revenue $ 54.6 $ 53.5 $ 107.2 $ 106.9
Project expenses 45.6 45.3 88.8 90.8
Project other expenses (0.3) (2.7) (2.5) (7.7)
Project income 8.7 5.5 15.9 8.4
Chambers
        
Operating results        
Project revenue 13.4 14.7 26.6 28.0
Project expenses 11.1 8.7 20.7 18.5
Project other expenses (0.6) (0.4) (1.2) (1.6)
Project income 1.7 5.6 4.7 7.9
Other
        
Operating results        
Project revenue 41.2 38.8 80.6 78.9
Project expenses 34.5 36.6 68.1 72.3
Project other expenses 0.3 (2.3) (1.3) (6.1)
Project income $ 7.0 $ (0.1) $ 11.2 $ 0.5