Employee Benefit Plans (Target and Actual Asset Allocations) (Details)	Dec. 31, 2020	Dec. 31, 2019
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

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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

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