Leases - Future Minimum Lease Payments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Total operating leases
2020	$ 6.8
2021	4.8
2022	4.8
2023	4.9
2024	4.8
Thereafter	30.1
Total minimum lease payments	56.2
Less: interest	(14.8)
Present value of minimum lease payments	41.4	$ 48.8
Less: short-term lease liabilities	(4.4)
Long-term lease liabilities	37.0
Finance leases
2020	9.3
2021	10.3
2022	5.1
2023	0.9
2024	0.9
Therafter	76.2
Total minimum lease payments	102.7
Less: interest	(56.8)
Present value of minimum lease payments	45.9		$ 23.3
Less: short-term lease liabilities	(6.3)
Long-term lease liabilities	39.6
Capital lease
Short-term liabilities under capital lease	4.9
Long-term liabilities under capital lease	18.4
Power Purchase Contract
Finance leases
2020	8.8
2021	9.4
2022	4.2
2023	0.0
2024	0.0
Therafter	0.0
Total minimum lease payments	22.4
Less: interest	(4.0)
Present value of minimum lease payments	18.4
Less: short-term lease liabilities	(6.3)
Long-term lease liabilities	12.1
Two Creeks Solar Project
Finance leases
2020	0.2
2021	0.2
2022	0.2
2023	0.2
2024	0.2
Therafter	22.8
Total minimum lease payments	23.8
Less: interest	(16.1)
Present value of minimum lease payments	7.7
Less: short-term lease liabilities	0.0
Long-term lease liabilities	7.7
Badger Hollow Solar Farm I
Finance leases
2020	0.3
2021	0.7
2022	0.7
2023	0.7
2024	0.7
Therafter	53.4
Total minimum lease payments	56.5
Less: interest	(36.7)
Present value of minimum lease payments	19.8
Less: short-term lease liabilities	0.0
Long-term lease liabilities	$ 19.8