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Employee Benefit Plans (Target and Actual Asset Allocations) (Details) | Dec. 31, 2020 | Dec. 31, 2019
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Master Trust |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 100.00% |
Actual asset allocation | 100.00% | 100.00%
Master Trust | Global equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 28.00% |
Actual asset allocation | 30.00% | 27.00%
Master Trust | Global private equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 1.00% |
Actual asset allocation | 1.00% | 1.00%
Master Trust | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 58.00% |
Actual asset allocation | 55.00% | 57.00%
Master Trust | Return seeking debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 4.00% |
Actual asset allocation | 5.00% | 5.00%
Master Trust | Hedge funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 3.00% |
Actual asset allocation | 3.00% | 3.00%
Master Trust | Real estate and cash |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 6.00% |
Actual asset allocation | 6.00% | 7.00%
OPEB |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 100.00% |
Actual asset allocation | 100.00% | 100.00%
OPEB | U.S. equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 30.00% |
Actual asset allocation | 36.00% | 35.00%
OPEB | Non-U.S. equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 6.00% |
Actual asset allocation | 6.00% | 9.00%
OPEB | Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 45.00% |
Actual asset allocation | 42.00% | 37.00%
OPEB | Real estate |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 2.00% |
Actual asset allocation | 2.00% | 2.00%
OPEB | Cash |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target allocation | 17.00% |
Actual asset allocation | 14.00% | 17.00%

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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=118257860&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=118255775&loc=d3e1928-114920 + Details
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- Definition Percentage of actual 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/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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