Consolidated Balance Sheet - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Current Assets [Abstract]
Cash and Cash Equivalents	$ 98.5	$ 98.9
Accounts Receivable (Less Allowance of $2.1 and $2.1)	128.2	135.1
Inventories – Net	143.1	95.9
Prepayments and Other	33.8	37.6
Total Current Assets	403.6	367.5
Property, Plant and Equipment – Net	3,786.1	3,822.4
Regulatory Assets	376.0	384.7
Investment in ATC	120.1	118.7
Other Investments	52.8	53.1
Goodwill and Intangible Assets – Net	224.5	225.9
Other Non-Current Assets	109.0	107.7
Total Assets	5,072.1	5,080.0
Current Liabilities [Abstract]
Accounts Payable	88.1	136.3
Accrued Taxes	60.5	50.0
Accrued Interest	14.6	17.6
Long-Term Debt Due Within One Year	106.2	64.1
Other	130.2	83.2
Total Current Liabilities	399.6	351.2
Long-Term Debt	1,396.5	1,439.2
Deferred Income Taxes	229.7	230.5
Regulatory Liabilities	516.0	532.0
Defined Benefit Pension and Other Postretirement Benefit Plans	175.2	191.8
Other Non-Current Liabilities	257.8	267.1
Total Liabilities	2,974.8	3,011.8
Commitments, Guarantees and Contingencies (Note 13)
Shareholders’ Equity [Abstract]
Common Stock Without Par Value, 80.0 Shares Authorized, 51.3 and 51.1 Shares Issued and Outstanding	1,407.4	1,401.4
Accumulated Other Comprehensive Loss	(27.9)	(22.6)
Retained Earnings	717.8	689.4
Total Shareholders’ Equity	2,097.3	2,068.2
Total Liabilities and Shareholders' Equity	$ 5,072.1	$ 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).

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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.