Consolidated Statement of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating Revenues [Abstract]
Contracts with Customers - Utility	$ 254.1	$ 261.3	$ 786.1	$ 789.3
Contracts with Customers - Non-utility	31.3	80.7	141.1	243.1
Other - Non-utility	2.9	6.0	8.7	17.9
Total Operating Revenue	288.3	348.0	935.9	1,050.3
Operating Expenses [Abstract]
Fuel, Purchased Power and Gas - Utility	98.2	103.2	295.9	300.6
Transmission Services - Utility	18.3	17.9	55.8	53.1
Cost of Sales - Non-utility	14.7	38.7	61.8	108.6
Operating and Maintenance	58.1	80.3	201.0	253.6
Depreciation and Amortization	49.5	51.5	151.6	153.4
Taxes Other than Income Taxes	12.5	13.1	39.8	43.8
Total Operating Expenses	251.3	304.7	805.9	913.1
Operating Income	37.0	43.3	130.0	137.2
Other Income (Expense) [Abstract]
Interest Expense	(16.1)	(17.6)	(48.9)	(51.6)
Equity Earnings	4.9	4.0	15.3	13.0
Gain on Sale of U.S. Water Services	0.0	0.0	20.6	0.0
Other	3.0	1.4	14.6	5.7
Total Other Income (Expense)	(8.2)	(12.2)	1.6	(32.9)
Income Before Income Taxes	28.8	31.1	131.6	104.3
Income Tax Expense (Benefit)	(2.4)	0.4	(4.3)	(8.7)
Net Income	$ 31.2	$ 30.7	$ 135.9	$ 113.0
Earnings Per Share [Abstract]
Basic (Shares)	51.7	51.4	51.6	51.3
Diluted (Shares)	51.8	51.6	51.7	51.5
Basic Earnings Per Share of Common Stock	$ 0.60	$ 0.59	$ 2.63	$ 2.20
Diluted Earnings Per Share of Common Stock	$ 0.60	$ 0.59	$ 2.63	$ 2.19