Commitments and Contingencies Commitments and Contingencies, Leases - Future Commitments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Operating Leases after Adoption of ASC Topic 842
2019	$ 81.2
2020	108.9
2021	108.4
2022	93.6
2023	80.9
Thereafter	317.8
Total minimum obligation	790.8
Interest component of obligation	(126.9)
Present value of minimum obligation	663.9
Less current portion	(82.8)
Operating Lease, Liability, Noncurrent	$ 581.1	$ 0.0
Weighted-average remaining lease term in years	8 years 4 months
Finance Leases after Adoption of ASC Topic 842
2019	$ 18.7
2020	24.8
2021	23.6
2022	20.5
2023	20.3
Thereafter	420.4
Total minimum obligation	528.3
Interest component of obligation	384.8
Present value of minimum obligation	143.5
Less current portion	(6.3)
Noncurrent operating and finance lease liabilities	$ 137.2
Weighted-average remaining lease term in years	39 years 2 months
Operating Leases before Adoption of ASC Topic 842
2019		106.3
2020		106.6
2021		105.9
2022		91.0
2023		78.1
Thereafter		342.0
Finance Leases before Adoption of ASC Topic 842
2019		24.9
2020		24.8
2021		23.6
2022		20.5
2023		20.3
Thereafter		420.4
Total minimum obligation		534.5
Interest component of obligation		(389.5)
Present value of minimum obligation		145.0
PPAs
Operating Leases after Adoption of ASC Topic 842
2019	$ 71.6
2020	95.9
2021	96.4
2022	82.6
2023	70.0
Thereafter	288.6
Total minimum obligation	705.1
Interest component of obligation	(112.4)
Present value of minimum obligation	592.7
Operating Leases before Adoption of ASC Topic 842
2019		95.5
2020		95.9
2021		96.4
2022		82.6
2023		70.0
Thereafter		288.6
Other
Operating Leases after Adoption of ASC Topic 842
2019	9.6
2020	13.0
2021	12.0
2022	11.0
2023	10.9
Thereafter	29.2
Total minimum obligation	85.7
Interest component of obligation	(14.5)
Present value of minimum obligation	$ 71.2
Operating Leases before Adoption of ASC Topic 842
2019		10.8
2020		10.7
2021		9.5
2022		8.4
2023		8.1
Thereafter		$ 53.4