Commitments and Contingencies - Analysis of lease liability maturities (Details) $ in Millions	Dec. 31, 2019 USD ($)
Operating Leases
2020	$ 7.6
2021	6.6
2022	3.3
2023	2.0
2024	2.3
Thereafter	4.3
Total undiscounted lease payments	26.1
Imputed interest	(2.5)
Debt financing costs	0.0
Total operating lease liabilities	23.6
Finance Leases
2020	22.2
2021	21.9
2022	725.4
2023	0.0
2024	0.0
Thereafter	0.0
Total undiscounted lease payments	769.5
Imputed interest	(50.1)
Debt financing costs	(5.5)
Total finance lease liabilities	$ 713.9