Fair Value (Gains (Losses) Related to the Trust) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Rabbi Trust
Schedule of Investments [Line Items]
Gains (losses) related to the trust	$ (3)	$ 37	$ (11)
Equity securities
Schedule of Investments [Line Items]
Gains (losses) related to the trust	(1)	27	(8)
Fixed Income Securities
Schedule of Investments [Line Items]
Gains (losses) related to the trust	$ (2)	$ 10	$ (3)

Amount of realized and unrealized gain (loss) on investment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
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