Significant Accounting Policies Income Taxes (Policies)	12 Months Ended
Significant Accounting Policies Income Taxes (Policies)	Dec. 31, 2017
Accounting Policies [Abstract]
Income Taxes	Income Taxes The provision for income taxes includes U.S. federal, state, local and foreign taxes. Income taxes are accounted for under the liability method. Deferred tax assets and liabilities are recognized for the estimated future tax consequences of temporary differences between the financial statement carrying amounts and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which the temporary differences are expected to be reversed. We evaluate the realizability of our deferred tax assets and establish a valuation allowance when it is “more likely than not” that all or a portion of the deferred tax assets will not be realized. We evaluate our tax positions using the “more likely than not” recognition threshold and then apply a measurement assessment to those positions that meet the recognition threshold. The factors used in assessing valuation allowances include all available evidence, such as past operating results, estimates of future taxable income and the feasibility of tax planning strategies. We have established tax reserves that we believe to be adequate in relation to the potential for additional assessments in each of the jurisdictions in which we are subject to taxation. We regularly assess the likelihood of additional tax assessments in those jurisdictions and adjust our reserves as additional information or events require. In response to the enactment of the Tax Act, the SEC issued SAB 118 on December 22, 2017, which acknowledges that the information necessary to determine such income tax effects may not be sufficiently available, prepared or analyzed in reasonable detail to complete the accounting under U.S. GAAP. SAB 118 allows for the reporting of provisional amounts for those specific tax effects for which a reasonable estimate can be made, and for no amounts to be recorded where a reasonable estimate cannot be made. Any subsequent adjustments to reported amounts will be made over the measurement period, which begins in the reporting period that includes the Tax Act's enactment date and ends when an entity has obtained, prepared and analyzed the information that is needed in order to complete the accounting requirements under U.S. GAAP, not to exceed one year from the enactment date. We have reasonably estimated and recorded provisional amounts resulting from the enactment of the Tax Act. Refer to Note 7 to our Consolidated Financial Statements for further information.

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.