Annual report pursuant to Section 13 and 15(d)

SEGMENT INFORMATION (Financial Information by Geographic Area) (Details)

v3.8.0.1
SEGMENT INFORMATION (Financial Information by Geographic Area) (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Operating revenue $ 838.5 $ 834.8 $ 856.7 $ 832.2 $ 801.1 $ 804.1 $ 811.3 $ 728.3 $ 3,362.2 $ 3,144.9 $ 2,663.6
Percentage of operating revenues                 100.00% 100.00% 100.00%
Long-lived assets 6,235.0       5,991.1       $ 6,235.0 $ 5,991.1  
Percentage of consolidated long-lived assets                 100.00% 100.00%  
U.S.                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Operating revenue                 $ 2,379.7 $ 2,290.9 $ 2,041.7
Percentage of operating revenues                 71.00% 73.00% 77.00%
Long-lived assets 3,274.5       3,282.5       $ 3,274.5 $ 3,282.5  
Percentage of consolidated long-lived assets                 53.00% 55.00%  
U.K.                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Operating revenue                 $ 311.2 $ 232.1 $ 224.1
Percentage of operating revenues                 9.00% 7.00% 8.00%
Long-lived assets 303.2       278.1       $ 303.2 $ 278.1  
Percentage of consolidated long-lived assets                 5.00% 5.00%  
Australia                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Operating revenue                 $ 304.0 $ 214.3 $ 5.0
Percentage of operating revenues                 9.00% 7.00%  
Long-lived assets 2,207.1       2,061.7       $ 2,207.1 $ 2,061.7  
Percentage of consolidated long-lived assets                 35.00% 34.00%  
Canada                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Operating revenue                 $ 148.9 $ 134.3 $ 135.5
Percentage of operating revenues                 4.00% 4.00% 5.00%
Long-lived assets 67.4       52.4       $ 67.4 $ 52.4  
Percentage of consolidated long-lived assets                 1.00% 1.00%  
Other                      
Revenues from External Customers and Long-Lived Assets [Line Items]                      
Operating revenue                 $ 218.4 $ 273.3 $ 257.3
Percentage of operating revenues                 7.00% 9.00% 10.00%
Long-lived assets $ 382.8       $ 316.4       $ 382.8 $ 316.4  
Percentage of consolidated long-lived assets                 6.00% 5.00%