STOCK-BASED COMPENSATION PLANS - Schedule of Stock-Based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	$ 51	$ 116	$ 143
Stock-based compensation costs capitalized	26	54	60
Incentive Plans \| Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	22	73	102
Incentive Plans \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	1	1	1
401(k) Savings Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	33	33	33
EDCP & DCPD
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation costs	$ (5)	$ 9	$ 7

Amount of cost capitalized for award under share-based payment arrangement.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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Amount of cost expensed and capitalized for award under share-based payment arrangement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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