Common Equity Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Equity [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 279.5	$ 52.7
Basic average common shares outstanding	200.2	200.1
Contingently issuable shares (performance and restricted stock units)	0.4	0.0
Diluted average common shares outstanding	200.6	200.1
Earnings Per Share, Basic and Diluted [Abstract]
Basic earnings per average common share	$ 1.40	$ 0.26
Diluted earnings per average common share	$ 1.39	$ 0.26
Anti-dilutive shares excluded from earnings per share calculation	0.0	0.0