Income Taxes - Components of Deferred Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred Tax Assets
Tax gross up - regulatory items	$ 438.6	$ 459.0
Future tax benefits	160.7	187.7
Deferred revenues	84.7	86.8
Other	168.3	190.2
Total deferred tax assets	852.3	923.7
Valuation allowance	(5.0)	(1.2)
Net deferred tax assets	847.3	922.5
Deferred Tax Liabilities
Property-related	4,198.0	4,072.5
Investment in affiliates	915.1	839.7
Employee benefits and compensation	227.2	219.5
Deferred costs - plant retirements	199.6	212.8
Other	225.9	203.6
Total deferred tax liabilities	5,765.8	5,548.1
Deferred tax liability, net	$ 4,918.5	$ 4,625.6