Consolidated Statement of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating Activities [Abstract]
Net Income	$ 64.5	$ 70.5
AFUDC – Equity	(0.5)	(0.6)
Income from Equity Investments – Net of Dividends	0.0	(1.2)
Realized and Unrealized (Gain) Loss on Investments and Property, Plant and Equipment	3.1	(2.2)
Depreciation Expense	53.4	50.7
Amortization of PSAs	(2.8)	(2.9)
Amortization of Other Intangible Assets and Other Assets	2.6	3.8
Deferred Income Tax Expense (Benefit)	(13.8)	2.6
Share-Based and ESOP Compensation Expense	1.7	1.8
Defined Benefit Pension and Postretirement Benefit Expense	0.0	1.1
Payments / Provision for Interim Rate Refund	0.0	0.6
Payments / Provision for Tax Reform Refund	0.0	(10.2)
Bad Debt Expense	0.4	0.4
Gain on Sale of U.S. Water Services	0.0	(20.1)
Changes in Operating Assets and Liabilities [Abstract]
Accounts Receivable	(3.4)	20.9
Inventories	(6.2)	(5.1)
Prepayments and Other	4.0	2.9
Accounts Payable	(5.5)	(5.5)
Other Current Liabilities	7.1	(9.1)
Cash Contributions to Defined Benefit Pension Plans	(10.7)	(10.4)
Changes in Regulatory and Other Non-Current Assets	(11.4)	0.0
Changes in Regulatory and Other Non-Current Liabilities	6.3	(8.9)
Cash from Operating Activities	88.8	79.1
Investing Activities [Abstract]
Proceeds from Sale of Available-for-sale Securities	0.9	2.7
Payments for Purchase of Available-for-sale Securities	(1.1)	(2.6)
Payments for Equity Investments	(27.8)	(0.5)
Return of Capital From Equity Investments	0.0	8.3
Proceeds from Sale of U.S. Water Services - Net of Transaction Costs and Cash Retained	0.0	264.7
Additions to Property, Plant and Equipment	(154.3)	(89.3)
Payments for (Proceeds from) Other Investing Activities	(0.2)	1.8
Cash from (for) Investing Activities	(182.5)	185.1
Financing Activities [Abstract]
Proceeds from Issuance of Common Stock	3.3	0.8
Proceeds from Issuance of Long-term Debt	110.0	100.0
Repayments of Long-Term Debt	(1.4)	(43.8)
Acquisition-Related Contingent Consideration Payments	0.0	(3.8)
Dividends on Common Stock	(31.9)	(30.3)
Other Financing Activities	0.1	(0.9)
Cash from Financing Activities	80.1	22.0
Change in Cash, Cash Equivalents and Restricted Cash	(13.6)	286.2
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 78.9	$ 365.2