Consolidated Statement of Income Consolidated Statement of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating Revenues [Abstract]
Contracts with Customers - Utility	$ 249.8	$ 257.8	$ 532.0	$ 528.0
Contracts with Customers - Non-utility	37.7	80.4	109.8	162.4
Other - Non-utility	2.9	5.9	5.8	11.9
Total Operating Revenue	290.4	344.1	647.6	702.3
Operating Expenses [Abstract]
Fuel, Purchased Power and Gas - Utility	87.9	96.5	197.7	197.4
Transmission Services - Utility	19.2	16.8	37.5	35.2
Cost of Sales - Non-utility	16.5	37.0	47.1	69.9
Operating and Maintenance	66.7	86.8	142.9	173.3
Depreciation and Amortization	50.2	56.1	102.1	101.9
Taxes Other than Income Taxes	13.7	14.4	27.3	30.7
Total Operating Expenses	254.2	307.6	554.6	608.4
Operating Income	36.2	36.5	93.0	93.9
Other Income (Expense) [Abstract]
Interest Expense	(16.3)	(17.1)	(32.8)	(34.0)
Equity Earnings	4.8	4.3	10.4	9.0
Gain on Sale of U.S. Water Services	0.5	0.0	20.6	0.0
Other	4.2	2.2	11.6	4.3
Total Other Income (Expense)	(6.8)	(10.6)	9.8	(20.7)
Income Before Income Taxes	29.4	25.9	102.8	73.2
Income Tax Expense (Benefit)	(4.8)	(5.4)	(1.9)	(9.1)
Net Income	$ 34.2	$ 31.3	$ 104.7	$ 82.3
Earnings Per Share [Abstract]
Basic (Shares)	51.6	51.3	51.6	51.2
Diluted (Shares)	51.7	51.5	51.7	51.4
Basic Earnings Per Share of Common Stock	$ 0.66	$ 0.61	$ 2.03	$ 1.61
Diluted Earnings Per Share of Common Stock	$ 0.66	$ 0.61	$ 2.02	$ 1.60