Consolidated Balance Sheet - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Current Assets [Abstract]
Cash and Cash Equivalents	$ 121.9	$ 98.9
Accounts Receivable (Less Allowance of $2.3 and $2.1)	132.4	135.1
Inventories – Net	145.4	95.9
Prepayments and Other	24.3	37.6
Total Current Assets	424.0	367.5
Property, Plant and Equipment – Net	3,809.3	3,822.4
Regulatory Assets	374.5	384.7
Investment in ATC	123.6	118.7
Other Investments	52.5	53.1
Goodwill and Intangible Assets – Net	225.8	225.9
Other Non-Current Assets	105.0	107.7
Total Assets	5,114.7	5,080.0
Current Liabilities [Abstract]
Accounts Payable	105.0	136.3
Accrued Taxes	42.0	50.0
Accrued Interest	18.0	17.6
Long-Term Debt Due Within One Year	56.7	64.1
Other	128.5	83.2
Total Current Liabilities	350.2	351.2
Long-Term Debt	1,462.2	1,439.2
Deferred Income Taxes	228.5	230.5
Regulatory Liabilities	516.0	532.0
Defined Benefit Pension and Other Postretirement Benefit Plans	175.2	191.8
Other Non-Current Liabilities	274.4	267.1
Total Liabilities	3,006.5	3,011.8
Commitments, Guarantees and Contingencies (Note 13)
Shareholders’ Equity [Abstract]
Common Stock Without Par Value, 80.0 Shares Authorized, 51.4 and 51.1 Shares Issued and Outstanding	1,415.4	1,401.4
Accumulated Other Comprehensive Loss	(27.6)	(22.6)
Retained Earnings	720.4	689.4
Total Shareholders’ Equity	2,108.2	2,068.2
Total Liabilities and Shareholders' Equity	$ 5,114.7	$ 5,080.0

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682