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Quarterly Financial Data (Tables) | 12 Months Ended
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Dec. 31, 2018
Quarterly Financial Data [Abstract] |
Schedule of Quarterly Financial Information |
|  | Three months ended |
(in millions except per share amounts) |  | March 31 |  | June 30 |  | Sept. 30 |  | Dec. 31 |
2018 |  |  |  |  |  |  |  |  |
Operating revenues |  | $ | 4,944 |  |  | $ | 5,742 |  |  | $ | 5,575 |  |  | $ | 5,704 |  |
Operating income |  | 616 |  |  | 972 |  |  | 798 |  |  | 820 |  |
Income before income taxes |  | 602 |  |  | 960 |  |  | 786 |  |  | 817 |  |
Net income |  | 463 |  |  | 733 |  |  | 615 |  |  | 654 |  |
Net income per share, basic |  | 0.79 |  |  | 1.27 |  |  | 1.08 |  |  | 1.17 |  |
Net income per share, diluted |  | 0.79 |  |  | 1.27 |  |  | 1.08 |  |  | 1.17 |  |
|  | March 31 |  | June 30 |  | Sept. 30 |  | Dec. 31 |
|  | As Recast |  | As Recast |  | As Recast |  | As Recast |
2017 |  |  |  |  |  |  |  |  |
Operating revenues |  | $ | 4,854 |  |  | $ | 5,731 |  |  | $ | 5,303 |  |  | $ | 5,258 |  |
Operating income |  | 606 |  |  | 1,215 |  |  | 845 |  |  | 741 |  |
Income before income taxes |  | 532 |  |  | 1,165 |  |  | 832 |  |  | 736 |  |
Net income |  | 339 |  |  | 743 |  |  | 528 |  |  | 1,747 |  | (a)
Net income per share, basic |  | 0.55 |  |  | 1.23 |  |  | 0.88 |  |  | 2.95 |  | (a)
Net income per share, diluted |  | 0.55 |  |  | 1.23 |  |  | 0.88 |  |  | 2.94 |  | (a)
(a) Includes a $1.3 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 Tabular disclosure of quarterly financial data. Includes, but is not limited to, financial information for fiscal quarters, cumulative effect of a change in accounting principle and earnings per share data. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=109225645&loc=d3e1280-108306 + Details
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