Income Taxes	6 Months Ended
Jun. 30, 2018
Income Taxes
Income Taxes	8. Income Taxes Our effective income tax rates for the three-month periods ended June 30, 2018 and 2017 were 24.0% and 31.2%, respectively. Our effective income tax rates for the six-month periods ended June 30, 2018 and 2017 were 24.0% and 32.0%, respectively. Our 2018 three-month and six-month period effective income tax rates were favorably impacted by the Tax Cuts and Jobs Act of 2017 (“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 six months ended June 30, 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 six months ended June 30, 2018.

8. Income Taxes

Our effective income tax rates for the three-month periods ended June 30, 2018 and 2017 were 24.0% and 31.2%, respectively. Our effective income tax rates for the six-month periods ended June 30, 2018 and 2017 were 24.0% and 32.0%, respectively. Our 2018 three-month and six-month period effective income tax rates were favorably impacted by the Tax Cuts and Jobs Act of 2017 (“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 six months ended June 30, 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 six months ended June 30, 2018.