| **Selected Quarterly Financial Data (Unaudited)**         | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
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| **Quarterly Financial Information Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| Selected Quarterly Financial Data (Unaudited)             | SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Millions of dollars)      2013 First quarter Second quarter Third quarter Fourth quarterTotal revenues $680 $694 $698 $711Profit before income taxes $187 $158 $165 $208Profit $141 $111 $118 $160         2012 First quarter Second quarter Third quarter Fourth quarterTotal revenues $668 $668 $678 $679Profit before income taxes $170 $144 $153 $124Profit $120 $104 $109 $99         2011 First quarter Second quarter Third quarter Fourth quarterTotal revenues $640 $675 $668 $662Profit before income taxes $115 $152 $126 $111Profit $83 $107 $93 $95          |

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| - Definition
The entire disclosure for the quarterly financial data in the annual financial statements.  The disclosure may include a tabular presentation of financial information for each fiscal quarter for the current and previous year, including revenues, gross profit, income or loss before extraordinary items and earnings per share data. It also includes an indication if the information in the note is unaudited, comments on the aggregate effect of year-end adjustments, and an explanation of matters or transactions that affect comparability or are pertinent to an understanding of the information furnished.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 45 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6372559&loc=d3e765-108305Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6372559&loc=d3e725-108305Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a)-(j) -URI http://asc.fasb.org/extlink&oid=25249566&loc=d3e1280-108306Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 6 -Section G -Subsection 1Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-K (SK) -Number 229 -Section 302 -Paragraph a
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