CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
CASH FLOWS FROM OPERATING ACTIVITES [Abstract]
Net income	$ 142.0	$ 132.1
Adjustments to reconcile net income to cash from operating activities:
Depreciation & amortization	193.4	191.6
Deferred income taxes & investment tax credits	68.9	44.6
Equity in (losses) of unconsolidated affiliates	0.2	0.6
Provision for uncollectible accounts	5.3	5.9
Expense portion of pension & postretirement benefit cost	2.9	4.7
Other non-cash items - net	2.0	6.3
Changes in working capital accounts [Abstract]
Accounts receivable & accrued unbilled revenues	42.3	17.8
Inventories	(3.6)	(11.8)
Recoverable/refundable fuel & natural gas costs	(30.8)	27.1
Prepayments & other current assets	15.0	46.9
Accounts payable, including to affiliated companies	(7.9)	(36.5)
Accrued liabilities	1.2	(1.9)
Unconsolidated Affiliate Dividends	0.2	0.8
Employer contributions to pension & postretirement plans	(18.6)	(23.3)
Changes in noncurrent assets	(32.0)	(15.8)
Changes in noncurrent liabilities	(2.2)	(2.5)
Net cash provided by operating activities	378.3	386.6
Proceeds from:
Long-term debt, net of issuance costs	0.0	37.5
Dividend reinvestment plan & other common stock issuances	4.6	4.7
Requirements for:
Dividends on common stock	(99.4)	(94.3)
Retirement of long-term debt	(73.0)	(5.0)
Net change in short-term borrowings	116.7	(45.4)
Net cash used in financing activities	(51.1)	(102.5)
Proceeds from:
Sale of assets and other collections	16.6	7.4
Requirements for:
Capital expenditures, excluding AFUDC equity	(381.9)	(349.4)
Business Acquisitions and Other Costs	(4.7)	(14.0)
Changes in Restricted Cash	2.5	(9.7)
Net cash used in investing activities	(367.5)	(365.7)
Net change in cash & cash equivalents	(40.3)	(81.6)
Cash & cash equivalents at beginning of period	74.7	86.4
Cash & cash equivalents at end of period	$ 34.4	$ 4.8