Other Income, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Income and Expenses [Abstract]
Non-service components of net periodic benefit costs	$ 41.2	$ 36.2	$ 26.0
AFUDC – Equity	20.9	14.4	15.2
Gains (losses) from investments held in rabbi trust	12.7	21.2	(1.8)
Other, net	4.7	30.4	30.9
Other income, net	$ 79.5	$ 102.2	$ 70.3