v3.19.3.a.u2
PPAs and other definite-lived intangible assets and liabilities (Details) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Components of intangible assets    
Assets, gross balance at the end of the period $ 365.6 $ 362.7
Less: accumulated amortization (221.3) (192.6)
Assets, net balance at the end of the period 144.3 170.1
Liabilities, gross balances at the end of the period (40.7) (41.3)
Less: accumulated amortization 20.9 20.1
Liabilities, net balance at the end of the period (19.8) (21.2)
Power Purchase Agreements    
Components of intangible assets    
Assets, gross balance at the end of the period 365.6 362.7
Less: accumulated amortization (221.3) (192.6)
Assets, net balance at the end of the period 144.3 170.1
Liabilities, gross balances at the end of the period (28.1) (28.7)
Less: accumulated amortization 14.4 14.0
Liabilities, net balance at the end of the period (13.7) (14.7)
Fuel Supply Agreements    
Components of intangible assets    
Liabilities, gross balances at the end of the period (12.6) (12.6)
Less: accumulated amortization 6.5 6.1
Liabilities, net balance at the end of the period $ (6.1) $ (6.5)