Commitments and Contingencies Leases (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Weighted Average Discount Rate, Percent	4.40%	4.40%
Maximum lease term for short-term lease classification		12 months
Operating Lease Right of Use Assets
Operating Lease, Right-of-Use Asset, Gross	$ 548.3	$ 548.3
Operating Lease, Right-of-Use Asset, Accumulated Depreciation	(19.3)	(19.3)
Operating Lease, Right-of-Use Asset	529.0	529.0	$ 0.0
Operating Leases
Total operating lease expense	12.6	40.5
Short-term lease expense	0.3	1.2
Operating Leases after Adoption of ASC Topic 842
2019	12.4	12.4
2020	49.6	49.6
2021	49.5	49.5
2022	49.6	49.6
2023	49.6	49.6
Thereafter	505.6	505.6
Total minimum obligation	716.3	716.3
Interest component of obligation	(187.3)	(187.3)
Present value of minimum obligation	529.0	529.0
Less current portion	(26.8)	(26.8)
Noncurrent operating lease liabilities	$ 502.2	$ 502.2	0.0
Weighted-average remaining lease term in years	14 years 4 months	14 years 4 months
Operating Leases before Adoption of ASC 842
2019			51.9
2020			51.4
2021			51.3
2022			51.3
2023			51.3
Thereafter			507.1
PPAs
Operating Lease Right of Use Assets
Operating Lease, Right-of-Use Asset, Gross	$ 500.3	$ 500.3
Operating Leases
Total operating lease expense	11.4	36.8
Operating Leases after Adoption of ASC Topic 842
2019	11.6	11.6
2020	46.2	46.2
2021	46.2	46.2
2022	46.2	46.2
2023	46.2	46.2
Thereafter	450.8	450.8
Total minimum obligation	647.2	647.2
Interest component of obligation	(165.3)	(165.3)
Present value of minimum obligation	481.9	481.9
Operating Leases before Adoption of ASC 842
2019			46.7
2020			46.2
2021			46.2
2022			46.2
2023			46.2
Thereafter			450.8
Other
Operating Lease Right of Use Assets
Operating Lease, Right-of-Use Asset, Gross	48.0	48.0
Operating Leases
Total operating lease expense	1.2	3.7
Operating Leases after Adoption of ASC Topic 842
2019	0.8	0.8
2020	3.4	3.4
2021	3.3	3.3
2022	3.4	3.4
2023	3.4	3.4
Thereafter	54.8	54.8
Total minimum obligation	69.1	69.1
Interest component of obligation	(22.0)	(22.0)
Present value of minimum obligation	$ 47.1	$ 47.1
Operating Leases before Adoption of ASC 842
2019			5.2
2020			5.2
2021			5.1
2022			5.1
2023			5.1
Thereafter			$ 56.3