Consolidated Balance Sheet - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Current Assets [Abstract]
Cash and Cash Equivalents	$ 104.4	$ 27.5
Accounts Receivable (Less Allowance of $2.1 and $3.1)	136.7	122.5
Inventories – Net	102.6	104.2
Prepayments and Other	44.2	40.3
Total Current Assets	387.9	294.5
Property, Plant and Equipment – Net	3,746.3	3,741.2
Regulatory Assets	310.6	330.1
Investment in ATC	146.0	135.6
Other Investments	55.8	55.6
Goodwill and Intangible Assets – Net	228.9	213.4
Other Non-Current Assets	103.0	106.5
Total Assets	4,978.5	4,876.9
Current Liabilities [Abstract]
Accounts Payable	75.3	74.0
Accrued Taxes	51.8	46.5
Accrued Interest	14.6	17.6
Long-Term Debt Due Within One Year	64.1	187.7
Other	84.7	73.7
Total Current Liabilities	290.5	399.5
Long-Term Debt	1,444.6	1,370.4
Deferred Income Taxes	592.9	554.6
Regulatory Liabilities	111.5	125.8
Defined Benefit Pension and Other Postretirement Benefit Plans	195.2	210.9
Other Non-Current Liabilities	301.1	322.7
Total Liabilities	2,935.8	2,983.9
Commitments, Guarantees and Contingencies (Note 13)
Shareholders’ Equity [Abstract]
Common Stock Without Par Value, 80.0 Shares Authorized, 51.0 and 49.6 Shares Issued and Outstanding	1,394.3	1,295.3
Accumulated Other Comprehensive Loss	(26.9)	(28.2)
Retained Earnings	675.3	625.9
Total Shareholders’ Equity	2,042.7	1,893.0
Total Liabilities and Shareholders' Equity	$ 4,978.5	$ 4,876.9

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Name:	us-gaap_AccountsPayableCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.