INCOME STATEMENTS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Operating revenues	$ 1,520.9	$ 1,407.1	$ 1,411.9
Operating expenses
Cost of sales	597.2	458.3	540.6
Other operation and maintenance	406.4	426.3	396.2
Depreciation and amortization	188.6	174.3	166.2
Property and revenue taxes	39.9	40.0	41.3
Total operating expenses	1,232.1	1,098.9	1,144.3
Operating income	288.8	308.2	267.6
Other income, net	38.2	31.4	39.6
Interest expense	64.7	63.5	63.4
Other expense	(26.5)	(32.1)	(23.8)
Income before income taxes	262.3	276.1	243.8
Income tax expense	31.2	54.5	59.1
Net income	$ 231.1	$ 221.6	$ 184.7