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INCOME TAXES | 12 Months Ended
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Dec. 31, 2017
Income Tax Disclosure [Abstract] |
INCOME TAXES | INCOME TAXES Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The Tax Cuts and Jobs Act (the "Act") was enacted on December 22, 2017. The Act reduces the U.S. federal corporate tax rate from the previous rate of 35 percent to 21 percent, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred, and creates new taxes on certain foreign sourced earnings. At December 31, 2017, the Company has calculated the accounting for the tax effects of enactment of the Act as written, and made a reasonable estimate of the effects on the existing deferred tax balances. The Company will continue to refine the calculations as additional analysis is completed. In addition, these estimates may also be affected as the Company gains a more thorough understanding of the tax law, including those related to the deductibility of purchased assets, state tax treatment, and amounts related to Employee compensation. This re-measurement in 2017 resulted in a reduction in the Company's net deferred tax liability, as noted by the change in federal statutory tax rate as noted in the provision for income taxes below. The components of deferred tax assets and liabilities at December 31, 2017 and 2016, are as follows:
(in millions) |  | 2017 |  | 2016
DEFERRED TAX LIABILITIES: |  |  |  |
Accelerated depreciation |  | $ | 3,193 |  |  | $ | 4,726 |
Other |  | 86 |  |  | 134 |
Total deferred tax liabilities |  | 3,279 |  |  | 4,860 |
DEFERRED TAX ASSETS: |  |  |  |
Fuel derivative instruments |  | 12 |  |  | 233 |
Construction obligation |  | 326 |  |  | 402 |
Accrued employee benefits |  | 309 |  |  | 451 |
Other |  | 274 |  |  | 400 |
Total deferred tax assets |  | 921 |  |  | 1,486 |
Net deferred tax liability |  | $ | 2,358 |  |  | $ | 3,374 |
The provision for income taxes is composed of the following:
(in millions) |  | 2017 |  | 2016 |  | 2015
CURRENT: |  |  |  |  |  |
Federal |  | $ | 904 |  |  | $ | 778 |  |  | $ | 1,292 |
State |  | 72 |  |  | 69 |  |  | 114 |
Total current |  | 976 |  |  | 847 |  |  | 1,406 |
DEFERRED: |  |  |  |  |  |
Federal |  | 192 |  |  | 426 |  |  | (97 | )
State |  | 5 |  |  | 30 |  |  | (11 | )
Change in federal statutory tax rate |  | (1,410 | ) |  | — |  |  | — |
Total deferred |  | (1,213 | ) |  | 456 |  |  | (108 | )
|  | $ | (237 | ) |  | $ | 1,303 |  |  | $ | 1,298 |
The effective tax rate on income before income taxes differed from the federal income tax statutory rate for the following reasons:
(in millions) |  | 2017 |  | 2016 |  | 2015
Tax at statutory U.S. tax rates |  | $ | 1,138 |  |  | $ | 1,241 |  |  | $ | 1,218 |
State income taxes, net of federal benefit |  | 50 |  |  | 64 |  |  | 66 |
Change in federal statutory tax rate |  | (1,410 | ) |  | — |  |  | — |
Other, net |  | (15 | ) |  | (2 | ) |  | 14 |
Total income tax provision |  | $ | (237 | ) |  | $ | 1,303 |  |  | $ | 1,298 |
The only periods subject to examination for the Company’s federal tax return are the 2016 and 2017 tax years.

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- Definition The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -URI http://asc.fasb.org/topic&trid=2144680 + Details
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