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QUARTERLY FINANCIAL DATA | 12 Months Ended
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Dec. 31, 2017
Quarterly Financial Data [Abstract] |
QUARTERLY FINANCIAL DATA | QUARTERLY FINANCIAL DATA (unaudited)
|  | Three months ended |
(in millions except per share amounts) |  | March 31 |  | June 30 |  | Sept. 30 |  | Dec. 31 |
2017 |  |  |  |  |  |  |  |  |
Operating revenues |  | $ | 4,883 |  |  | $ | 5,744 |  |  | $ | 5,271 |  |  | $ | 5,274 |  |
Operating income |  | 658 |  |  | 1,250 |  |  | 834 |  |  | 773 |  |
Income before income taxes |  | 553 |  |  | 1,170 |  |  | 791 |  |  | 737 |  |
Net income |  | 351 |  |  | 746 |  |  | 503 |  |  | 1,888 |  | (a)
Net income per share, basic |  | 0.57 |  |  | 1.24 |  |  | 0.84 |  |  | 3.19 |  | (a)
Net income per share, diluted |  | 0.57 |  |  | 1.23 |  |  | 0.84 |  |  | 3.18 |  | (a)
|  | March 31 |  | June 30 |  | Sept. 30 |  | Dec. 31 |
2016 |  |  |  |  |  |  |  |  |
Operating revenues |  | $ | 4,826 |  |  | $ | 5,384 |  |  | $ | 5,139 |  |  | $ | 5,076 |  |
Operating income |  | 944 |  |  | 1,276 |  |  | 695 |  |  | 846 |  |
Income before income taxes |  | 816 |  |  | 1,304 |  |  | 618 |  |  | 809 |  |
Net income |  | 513 |  |  | 820 |  |  | 388 |  |  | 522 |  |
Net income per share, basic |  | 0.80 |  |  | 1.30 |  |  | 0.63 |  |  | 0.85 |  |
Net income per share, diluted |  | 0.79 |  |  | 1.28 |  |  | 0.62 |  |  | 0.84 |  |
(a) Includes a $1.4 billion reduction in Provision for income taxes related to the Tax Cuts and Jobs Act legislation enacted in December 2017, which resulted in a re-measurement of the Company's deferred tax assets and liabilities at the new federal corporate tax rate of 21 percent. See Note 14 to the Consolidated Financial Statements for further information.

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- Definition The entire disclosure for quarterly financial data. Includes, but is not limited to, tabular presentation of financial information for fiscal quarters, effect of year-end adjustments, and an explanation of matters or transactions that affect comparability of the information. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -URI http://asc.fasb.org/topic&trid=2126967 + Details
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