Defined Benefit Postretirement Plans and Defined Contribution Plan - Health Care Cost Trends Table and Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($)
Pension Plan [Member]
Defined Benefit Plan Assumed Health Care Cost Trend Rates [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 20
Equity Securities [Member]
Defined Benefit Plan Assumed Health Care Cost Trend Rates [Line Items]
Target allocation percentage	55.00%
Fixed Income Securities [Member]
Defined Benefit Plan Assumed Health Care Cost Trend Rates [Line Items]
Target allocation percentage	45.00%

Amount after tax of reclassification adjustments of other comprehensive income (loss).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 17B
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL34724394-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=118951672&loc=d3e1436-108581

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