Income Taxes	3 Months Ended
Mar. 31, 2018
Income Taxes
Income Taxes	8. Income Taxes Our effective income tax rates for the first quarters of 2018 and 2017 were 24.0% and 32.7%, respectively. Our first quarter of 2018 effective income tax rate was favorably impacted by Tax Reform, which included significant changes to the taxation of U.S. corporations, including a reduction of the U.S. federal statutory rate from 35% to 21% effective January 1, 2018. Based on our preliminary assessment of the impact of Tax Reform, we recognized a one-time, provisional net tax benefit of $207.3 million in the fourth quarter of 2017, primarily related to the remeasurement of deferred tax assets and liabilities at the lowered federal statutory tax rate, which was partially offset by repatriation and related liabilities. Given the substantial changes to the Internal Revenue Code as a result of Tax Reform, our estimated financial impacts from Tax Reform are subject to further analysis, interpretation and clarification of the new law, which could result in changes to our estimates in future quarters in 2018. We did not make an adjustment during the first quarter of 2018 to our provisional estimate recognized in 2017. State income taxes offset by the effects of company-owned life insurance policies mainly accounted for the difference between our effective income tax rate and the federal statutory rate for the first quarter of 2018.

8. Income Taxes

Our effective income tax rates for the first quarters of 2018 and 2017 were 24.0% and 32.7%, respectively. Our first quarter of 2018 effective income tax rate was favorably impacted by Tax Reform, which included significant changes to the taxation of U.S. corporations, including a reduction of the U.S. federal statutory rate from 35% to 21% effective January 1, 2018. Based on our preliminary assessment of the impact of Tax Reform, we recognized a one-time, provisional net tax benefit of $207.3 million in the fourth quarter of 2017, primarily related to the remeasurement of deferred tax assets and liabilities at the lowered federal statutory tax rate, which was partially offset by repatriation and related liabilities. Given the substantial changes to the Internal Revenue Code as a result of Tax Reform, our estimated financial impacts from Tax Reform are subject to further analysis, interpretation and clarification of the new law, which could result in changes to our estimates in future quarters in 2018. We did not make an adjustment during the first quarter of 2018 to our provisional estimate recognized in 2017. State income taxes offset by the effects of company-owned life insurance policies mainly accounted for the difference between our effective income tax rate and the federal statutory rate for the first quarter of 2018.