Consolidated Statement of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating Activities [Abstract]
Net Income	$ 65.1	$ 81.4
AFUDC – Equity	(1.1)	(1.4)
Income from Equity Investments – Net of Dividends	1.1	(2.2)
Realized and Unrealized (Gain) Loss on Investments and Property, Plant and Equipment	(0.7)	1.1
Depreciation Expense	115.8	107.9
Amortization of PSAs	(5.7)	(5.6)
Amortization of Other Intangible Assets and Other Assets	5.1	4.6
Deferred Income Tax Benefit	(14.4)	(22.3)
Share-Based and ESOP Compensation Expense	3.1	3.1
Defined Benefit Pension and Postretirement Benefit Expense	2.2	0.0
Provision for Interim Rate Refund	0.0	11.7
Provision for Tax Reform Refund	0.0	(0.1)
Bad Debt Expense	0.6	1.1
Changes in Operating Assets and Liabilities [Abstract]
Accounts Receivable	5.7	9.5
Inventories	(13.9)	(9.3)
Prepayments and Other	1.7	3.3
Accounts Payable	(1.2)	(11.6)
Other Current Liabilities	(13.0)	(8.5)
Cash Contributions to Defined Benefit Pension Plans	(10.3)	(10.7)
Changes in Regulatory and Other Non-Current Assets	(25.6)	(16.8)
Changes in Regulatory and Other Non-Current Liabilities	(8.8)	8.1
Cash from Operating Activities	105.7	143.3
Investing Activities [Abstract]
Proceeds from Sale of Available-for-sale Securities	2.6	2.1
Payments for Purchase of Available-for-sale Securities	(2.0)	(2.3)
Payments for Equity Method Investments	(17.1)	(66.6)
Additions to Property, Plant and Equipment	(293.4)	(419.9)
Other Investing Activities	4.2	0.5
Cash for Investing Activities	(305.7)	(486.2)
Financing Activities [Abstract]
Proceeds from Issuance of Common Stock	10.1	7.9
Proceeds from Issuance of Short-Term and Long-Term Debt	379.0	297.4
Repayments of Short-Term and Long-Term Debt	(149.3)	(20.9)
Proceeds from Non-controlling Interest in Subsidiaries	28.9	67.8
Dividends on Common Stock	(65.7)	(63.9)
Other Financing Activities	(0.9)	(0.5)
Cash from Financing Activities	202.1	287.8
Change in Cash, Cash Equivalents and Restricted Cash	2.1	(55.1)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 67.3	$ 37.4