Income Taxes - Components of Deferred Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Deferred Tax Assets
Tax gross up - regulatory items	$ 420.1	$ 438.6
Future tax benefits	165.4	160.7
Deferred revenues	76.0	84.7
Other	167.9	168.3
Total deferred tax assets	829.4	852.3
Valuation allowance	(1.1)	(5.0)
Net deferred tax assets	828.3	847.3
Deferred Tax Liabilities
Property-related	4,545.2	4,198.0
Investment in affiliates	1,103.9	915.1
Employee benefits and compensation	231.4	227.2
Deferred costs - plant retirements	194.3	199.6
Other	268.2	225.9
Total deferred tax liabilities	6,343.0	5,765.8
Deferred tax liability, net	$ 5,514.7	$ 4,918.5