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FAIR VALUE MEASUREMENTS - Proceeds from the Sale of Investments (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Fair Value Disclosures [Abstract] |  |  |
Sale Proceeds | $ 186 | $ 1,637 | $ 800
Realized Gains | 12 | 98 | 41
Realized Losses | (8) | (31) | (48)
Interest and Dividend Income | $ 22 | $ 38 | $ 41

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