v3.5.0.2
Fair value of financial instruments - recurring (Details) - USD ($)
$ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2016
Dec. 31, 2015
Assets:    
Restricted cash $ 12.6 $ 15.2
Recurring    
Assets:    
Cash and cash equivalents 93.8 72.4
Restricted cash 12.6 15.2
Derivative instruments asset 2.9 0.3
Total 109.3 87.9
Liabilities:    
Derivative instruments liability 42.5 57.5
Total 42.5 57.5
Recurring | Credit valuation adjustments    
Liabilities:    
Net increase in fair value 5.2 3.8
Pre-tax gain in other comprehensive income 0.5 0.4
Gain in change in fair value of derivatives 4.7 3.4
Recurring | Level 1    
Assets:    
Cash and cash equivalents 93.8 72.4
Restricted cash 12.6 15.2
Total 106.4 87.6
Recurring | Level 2    
Assets:    
Derivative instruments asset 2.9 0.3
Total 2.9 0.3
Liabilities:    
Derivative instruments liability 42.5 57.5
Total $ 42.5 $ 57.5