v3.3.1.900
Fair value of financial instruments - recurring (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Assets:    
Cash and cash equivalents   $ 106.0
Restricted cash $ 15.2 22.5
Derivative instruments asset   1.1
Total   129.6
Liabilities:    
Derivative instruments liability   83.6
Total   83.6
Credit valuation adjustments    
Liabilities:    
Net increase in fair value 3.8 13.0
Pre-tax gain in other comprehensive income 0.4 0.7
Gain in change in fair value of derivatives 3.4 12.3
Recurring    
Assets:    
Cash and cash equivalents 72.4  
Restricted cash 15.2  
Derivative instruments asset 0.3  
Total 87.9  
Liabilities:    
Derivative instruments liability 57.5  
Total 57.5  
Recurring | Level 1    
Assets:    
Cash and cash equivalents 72.4 106.0
Restricted cash 15.2 22.5
Total 87.6 128.5
Recurring | Level 2    
Assets:    
Derivative instruments asset 0.3 1.1
Total 0.3 1.1
Liabilities:    
Derivative instruments liability 57.5 83.6
Total $ 57.5 $ 83.6