Statements Of Consolidated Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Income	$ 331.5	$ 302.1	$ 530.0
Adjustments to Reconcile Net Income to Net Cash from Continuing Operations:
Loss on early extinguishment of debt	0.0	97.2	0.0
Depreciation and amortization	547.1	524.4	486.9
Deferred income taxes and investment tax credits	182.3	135.3	161.4
Stock compensation expense and 401(k) profit sharing contribution	46.5	50.7	66.0
Income from discontinued operations - net of taxes	(3.4)	(103.5)	(273.8)
Amortization of discount/premium on debt	7.6	8.7	10.0
AFUDC equity	(11.6)	(11.5)	(10.7)
Other adjustments	(3.8)	13.1	6.3
Changes in Assets and Liabilities:
Accounts receivable	(188.0)	262.2	(42.8)
Inventories	38.9	46.9	(115.9)
Accounts payable	108.8	(190.5)	29.9
Customer deposits and credits	(52.3)	35.5	29.8
Taxes accrued	12.1	8.7	4.5
Interest accrued	(8.7)	(11.6)	4.3
Exchange gas receivable/payable	36.9	(31.7)	(43.9)
Other accruals	(6.0)	(55.1)	4.4
Prepayments and other current assets	(0.4)	0.1	(2.2)
Regulatory assets/liabilities	(187.9)	82.0	(227.7)
Postretirement and postemployment benefits	(44.8)	25.6	136.0
Deferred charges and other noncurrent assets	(1.2)	5.2	3.9
Other noncurrent liabilities	0.5	(30.4)	4.8
Net Operating Activities from Continuing Operations	804.1	1,163.4	761.2
Net Operating Activities from (used for) Discontinued Operations	(0.8)	293.4	558.4
Net Cash Flows from Operating Activities	803.3	1,456.8	1,319.6
Net Cash Provided by (Used in) Investing Activities [Abstract]
Capital expenditures	(1,475.2)	(1,360.7)	(1,282.5)
Restricted cash withdrawals (deposits)	20.1	(4.8)	(17.1)
Cash Contributions from Spin Off	0.0	3,798.2	0.0
Cost of removal	(110.1)	(79.2)	(46.5)
Other investing activities	(17.7)	21.5	32.6
Net Investing Activities from (used for) Continuing Operations	(1,582.9)	2,375.0	(1,313.5)
Net Investing Activities used for Discontinued Operations	0.0	(430.1)	(803.1)
Net Cash Flows from (used for) Investing Activities	(1,582.9)	1,944.9	(2,116.6)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Cash of CPG at Separation	0.0	(136.8)	0.0
Issuance of long-term debt	500.0	0.0	748.4
Repayments of long-term debt and capital lease obligations	(434.6)	(2,092.2)	(521.0)
Premiums and other debt related costs	(3.7)	(93.5)	(8.7)
Change in short-term borrowings, net	920.6	(936.4)	878.1
Issuance of common stock	23.1	22.5	30.3
Acquisition of treasury stock	(9.4)	(20.4)	(10.2)
Dividends paid - common stock	(205.5)	(263.4)	(321.3)
Net Financing Activities from (used for) Continuing Operations	790.5	(3,520.2)	795.6
Net Financing Activities from Discontinued Operations	0.0	108.6	0.0
Net Cash Flows from (used for) Financing Activities	790.5	(3,411.6)	795.6
Change in cash and cash equivalents from continuing operations	11.7	18.2	243.3
Change in cash and cash equivalents used for discontinued operations	(0.8)	(28.1)	(244.7)
Change in cash included in discontinued operations	0.0	0.5	(0.2)
Cash and cash equivalents at beginning of period	15.5	24.9	26.5
Cash and cash equivalents at beginning of period	$ 26.4	$ 15.5	$ 24.9