CONDENSED CONSOLIDATED INCOME STATEMENTS - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Operating revenues	$ 884.1	$ 924.0	$ 2,636.6	$ 2,721.7
Operating expenses
Cost of sales	300.6	316.5	911.3	944.4
Other operation and maintenance	260.1	384.7	753.3	1,086.9
Depreciation and amortization	96.2	87.4	287.4	259.6
Property and revenue taxes	26.1	27.6	78.0	82.1
Total operating expenses	683.0	816.2	2,030.0	2,373.0
Operating income	201.1	107.8	606.6	348.7
Other income, net	5.8	5.1	17.2	16.2
Interest expense	119.3	29.9	358.8	88.8
Other expense	(113.5)	(24.8)	(341.6)	(72.6)
Income before income taxes	87.6	83.0	265.0	276.1
Income tax benefit	(13.3)	(20.5)	(36.1)	(26.6)
Net income	100.9	103.5	301.1	302.7
Preferred stock dividend requirements	0.3	0.3	0.9	0.9
Net income attributed to common shareholder	$ 100.6	$ 103.2	$ 300.2	$ 301.8