Condensed Balance Sheets Parenthetical (USD $) In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
ASSETS
Accumulated depreciation	$ 1,357.9	$ 1,330.7	$ 1,287.3
Shareholders' equity:
Common stock, par value	$ 1.00	$ 1.00	$ 1.00
Common stock, authorized	120.0us-gaap_CommonStockSharesAuthorized	120.0us-gaap_CommonStockSharesAuthorized	120.0us-gaap_CommonStockSharesAuthorized
Common stock, issued	77.5us-gaap_CommonStockSharesIssued	77.4us-gaap_CommonStockSharesIssued	79.0us-gaap_CommonStockSharesIssued
Common stock, outstanding	77.5us-gaap_CommonStockSharesOutstanding	77.4us-gaap_CommonStockSharesOutstanding	79.0us-gaap_CommonStockSharesOutstanding

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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