Income Taxes - Summary of income tax expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Current tax expense (benefit)	$ 93.9	$ 49.2	$ (37.9)
Deferred income taxes, net	111.0	182.2	167.7
ITCs	(4.6)	(3.5)	(4.8)
Total income tax expense	$ 200.3	$ 227.9	$ 125.0