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INCOME TAXES - Changes in Liability for Tax Uncertainties, Excluding Interest (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Income Tax Disclosure [Abstract] |  |  |
Liability for tax uncertainties | $ 4 | $ 8 |
Changes in liability for tax uncertainties, excluding interest |  |  |
Balance at beginning of year | 28 | 37 | $ 45
Additions for tax positions related to the current year | 23 | 3 | 4
Additions for tax positions of prior years | 0 | 1 | 3
Reductions for tax positions of prior years | (2) | (1) | (5)
Reductions due to statute lapse | (10) | (10) | (9)
Settlements, audit payments, refunds - net | 0 | (2) | (1)
Balance at end of year | $ 39 | $ 28 | $ 37

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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 10B -URI http://asc.fasb.org/extlink&oid=120406818&loc=SL37586934-109318 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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