Fair Value (Gains (Losses) Related to the Trust) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Rabbi Trust
Schedule of Investments [Line Items]
Gains (losses) related to the Trust	$ 2	$ 3	$ (7)	$ 27
Equity securities
Schedule of Investments [Line Items]
Gains (losses) related to the Trust	2	1	(4)	18
Fixed income securities
Schedule of Investments [Line Items]
Gains (losses) related to the Trust	$ 0	$ 2	$ (3)	$ 9

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
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