Income Taxes	9 Months Ended
Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes TDS’ effective tax rate on Income before income taxes for the three and nine months ended September 30, 2018, was 7.3% and 23.9%, respectively. The effective tax rate is lower than normal due primarily to an income tax accounting method change that accelerated tax depreciation on certain assets for the 2017 tax year, resulting in a discrete tax benefit recorded in the third quarter of 2018. The effective tax rate for the three and nine months ended September 30, 2017, was not meaningful due primarily to the recognition of a loss on impairment of goodwill during the third quarter of 2017. Due to difficulty in reliably projecting an annual tax rate, TDS calculated income taxes for the nine months ended September 30, 2017, based on an estimated year-to-date tax rate. In December 2017, the Tax Act was signed into law. Following the guidance of the FASB’s Accounting Standards Update 2018-05, Income Taxes: Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118, Income tax expense (benefit) for the year ended December 31, 2017, included a provisional estimate for the impact of the Tax Act on TDS’ 2017 depreciation deduction. TDS has now completed a full analysis of contracts and agreements related to fixed assets placed in service during 2017 and Income tax expense (benefit) for the three and nine months ended September 30, 2018, includes a benefit of $1 million and $4 million, respectively, related to this final adjustment.

Income Taxes

TDS’ effective tax rate on Income before income taxes for the three and nine months ended September 30, 2018, was 7.3% and 23.9%, respectively. The effective tax rate is lower than normal due primarily to an income tax accounting method change that accelerated tax depreciation on certain assets for the 2017 tax year, resulting in a discrete tax benefit recorded in the third quarter of 2018.

The effective tax rate for the three and nine months ended September 30, 2017, was not meaningful due primarily to the recognition of a loss on impairment of goodwill during the third quarter of 2017. Due to difficulty in reliably projecting an annual tax rate, TDS calculated income taxes for the nine months ended September 30, 2017, based on an estimated year-to-date tax rate.

In December 2017, the Tax Act was signed into law. Following the guidance of the FASB’s Accounting Standards Update 2018-05, Income Taxes: Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118, Income tax expense (benefit) for the year ended December 31, 2017, included a provisional estimate for the impact of the Tax Act on TDS’ 2017 depreciation deduction. TDS has now completed a full analysis of contracts and agreements related to fixed assets placed in service during 2017 and Income tax expense (benefit) for the three and nine months ended September 30, 2018, includes a benefit of $1 million and $4 million, respectively, related to this final adjustment.