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Benefit Plans and Other Postretirement Benefits, Postretirement Health Care Benefits (Details) - Other Postretirement Benefits Plan [Member] | Dec. 31, 2018 | Dec. 31, 2017
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Postretirement Health Care Benefits [Abstract] |  |
Target pension asset allocations (as a percent) | 100.00% | 100.00%
Equity Securities |  |
Postretirement Health Care Benefits [Abstract] |  |
Target pension asset allocations (as a percent) | 18.00% | 24.00%
Long-duration fixed income and interest rate swap securities |  |
Postretirement Health Care Benefits [Abstract] |  |
Target pension asset allocations (as a percent) | 0.00% | 0.00%
Short-to-intermediate fixed income securities |  |
Postretirement Health Care Benefits [Abstract] |  |
Target pension asset allocations (as a percent) | 70.00% | 60.00%
Alternative investments |  |
Postretirement Health Care Benefits [Abstract] |  |
Target pension asset allocations (as a percent) | 8.00% | 9.00%
Cash |  |
Postretirement Health Care Benefits [Abstract] |  |
Target pension asset allocations (as a percent) | 4.00% | 7.00%

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- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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