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Pension and other Post-Retirement Benefits - Investment Objectives (Details) - Defined benefits pension plans - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Pension and other PostRetirement Benefits, |  |
Employer contributions | $ 160 |
Contribution deposited in solvency reserve account | 3 |
Expected cash contributions | $ 174 |
Equities |  |
Pension and other PostRetirement Benefits, |  |
Plan asset allocation percentage | 56.00% | 59.00%
Equities | Canada |  |
Pension and other PostRetirement Benefits, |  |
Plan asset allocation percentage | 18.00% | 19.00%
Equities | United States |  |
Pension and other PostRetirement Benefits, |  |
Plan asset allocation percentage | 19.00% | 23.00%
Equities | Foreign |  |
Pension and other PostRetirement Benefits, |  |
Plan asset allocation percentage | 19.00% | 17.00%
Fixed income | Canada |  |
Pension and other PostRetirement Benefits, |  |
Plan asset allocation percentage | 39.00% | 39.00%
Real estate |  |
Pension and other PostRetirement Benefits, |  |
Plan asset allocation percentage | 100.00% | 100.00%
Real estate | Canada |  |
Pension and other PostRetirement Benefits, |  |
Plan asset allocation percentage | 5.00% | 2.00%
Maximum | Fixed income |  |
Pension and other PostRetirement Benefits, |  |
Plan asset allocation percentage | 44.00% |

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- Definition The estimate of the expected contributions to be made to a defined benefit plan for the next annual reporting period. [Refer: Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 147 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_147_b&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2017-01-01 -Paragraph 148 -Subparagraph d -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_148_d_iii&doctype=Standard -URIDate 2017-03-09 + Details
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