v3.4.0.3
Fair value of financial instruments - recurring (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2016
Dec. 31, 2015
Assets:    
Restricted cash $ 10.0 $ 15.2
Recurring    
Assets:    
Cash and cash equivalents 64.3 72.4
Restricted cash 10.0 15.2
Derivative instruments asset 0.6 0.3
Total 74.9 87.9
Liabilities:    
Derivative instruments liability 62.0 57.5
Total 62.0 57.5
Recurring | Credit valuation adjustments    
Liabilities:    
Net increase in fair value 5.1 3.8
Pre-tax gain in other comprehensive income 0.5 0.4
Gain in change in fair value of derivatives 4.6 3.4
Recurring | Level 1    
Assets:    
Cash and cash equivalents 64.3 72.4
Restricted cash 10.0 15.2
Total 74.3 87.6
Recurring | Level 2    
Assets:    
Derivative instruments asset 0.6 0.3
Total 0.6 0.3
Liabilities:    
Derivative instruments liability 62.0 57.5
Total $ 62.0 $ 57.5