Goodwill and Intangibles - Intangible Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Finite-Lived Intangible Liabilities
Amortization	$ 53.7	$ 50.6	$ 11.3
Period of amortization	5 years
Amortization to be recorded as an increase to operating revenues
Amortization to be recorded in the next five years
2025	$ 53.9
2026	55.1
2027	55.1
2028	55.1
2029	55.1
Amortization to be recorded as a decrease to other operation and maintenance
Amortization to be recorded in the next five years
2025	0.2
2026	0.2
2027	0.2
2028	0.2
2029	0.2
WECI
Finite-Lived Intangible Liabilities
Gross carrying amount	691.5	665.8
Accumulated Amortization	(124.7)	(71.0)
Net Carrying Amount	566.8	594.8
PPAs | WECI
Finite-Lived Intangible Liabilities
Gross carrying amount	679.6	653.9
Accumulated Amortization	(119.3)	(66.6)
Net Carrying Amount	$ 560.3	587.3
PPAs | Blooming Grove Wind Energy Center LLC, Tatanka Ridge Wind, LLC, Jayhawk Renewables, LLC, Thunderhead Wind LLC, Samson I Solar Energy Center LLC, Sapphire Sky Wind Energy LLCSky
Finite-Lived Intangible Liabilities
Weighted average useful life	11 years
Proxy revenue swap | WECI
Finite-Lived Intangible Liabilities
Gross carrying amount	$ 7.2	7.2
Accumulated Amortization	(4.2)	(3.5)
Net Carrying Amount	$ 3.0	3.7
Proxy revenue swap | Upstream Wind Energy LLC
Finite-Lived Intangible Liabilities
Weighted average useful life	4 years
Length of proxy revenue contract, in years	10 years
Interconnection agreements | WECI
Finite-Lived Intangible Liabilities
Gross carrying amount	$ 4.7	4.7
Accumulated Amortization	(1.2)	(0.9)
Net Carrying Amount	$ 3.5	$ 3.8
Interconnection agreements | Tatanka Ridge Wind LLC and Bishop Hill Energy III LLC
Finite-Lived Intangible Liabilities
Weighted average useful life	16 years