Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Current Assets [Abstract]
Cash and Cash Equivalents	$ 69.1	$ 98.9
Accounts Receivable (Less Allowance of $1.7 and $2.1)	144.4	135.1
Inventories – Net	86.7	95.9
Prepayments and Other	34.1	37.6
Total Current Assets	334.3	367.5
Property, Plant and Equipment – Net	3,904.4	3,822.4
Regulatory Assets	389.5	384.7
Equity Investments	161.1	118.7
Other Investments	49.1	53.1
Goodwill and Intangible Assets – Net	223.3	225.9
Other Non-Current Assets	103.3	107.7
Total Assets	5,165.0	5,080.0
Current Liabilities [Abstract]
Accounts Payable	149.8	136.3
Accrued Taxes	51.4	50.0
Accrued Interest	17.9	17.6
Long-Term Debt Due Within One Year	57.5	64.1
Other	128.5	83.2
Total Current Liabilities	405.1	351.2
Long-Term Debt	1,428.5	1,439.2
Deferred Income Taxes	223.6	230.5
Regulatory Liabilities	512.1	532.0
Defined Benefit Pension and Other Postretirement Benefit Plans	177.3	191.8
Other Non-Current Liabilities	262.6	267.1
Total Liabilities	3,009.2	3,011.8
Commitments, Guarantees and Contingencies (Note 11)
Shareholders' Equity [Abstract]
Common Stock Without Par Value, 80.0 Shares Authorized, 51.5 and 51.1 Shares Issued and Outstanding	1,428.5	1,401.4
Accumulated Other Comprehensive Loss	(27.3)	(22.6)
Retained Earnings	754.6	689.4
Total Shareholders' Equity	2,155.8	2,068.2
Total Liabilities and Shareholders' Equity	$ 5,165.0	$ 5,080.0