Fair Value (Gains (Losses) Related to the Trust) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Rabbi Trust
Schedule of Investments [Line Items]
Gains (losses) related to the Trust	$ 22	$ 7	$ (9)	$ 24
Equity securities
Schedule of Investments [Line Items]
Gains (losses) related to the Trust	16	4	(6)	17
Fixed income securities
Schedule of Investments [Line Items]
Gains (losses) related to the Trust	$ 6	$ 3	$ (3)	$ 7

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
-Name Accounting Standards Codification
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