Income Taxes - Components of deferred income taxes (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Non-current
Tax gross up - regulatory items	$ 469.5	$ 497.6
Future tax benefits	104.6	102.5
Deferred revenues	97.8	104.2
Other	205.9	197.2
Total deferred tax assets	877.8	901.5
Valuation allowance	(1.2)	(2.3)
Net deferred tax assets	876.6	899.2
Non-current
Property-related	3,909.0	3,721.0
Investment in affiliates	648.6	647.2
Deferred costs - plant retirements	223.9	255.4
Employee benefits and compensation	170.6	148.2
Other	233.0	187.2
Total deferred tax liabilities	5,185.1	4,959.0
Deferred tax liability, net	$ 4,308.5	$ 4,059.8