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PENSION AND OTHER POST-EMPLOYMENT BENEFITS - Pension Investments Measured at Fair Value (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Pension |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 8,852 | $ 8,219
Asset Allocation | 100.00% | 100.00%
Excluded from total investments | $ 116 | $ 176
Pension | Investments Excluding in Investments at NAV |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 6,604 | $ 6,333
Asset Allocation | 75.00% | 78.00%
Pension | Cash and short-term securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 1,493 | $ 1,069
Asset Allocation | 17.00% | 13.00%
Pension | Equity securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 2,065 | $ 2,360
Asset Allocation | 23.00% | 29.00%
Pension | Corporate debt securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 2,672 | $ 2,064
Asset Allocation | 31.00% | 25.00%
Pension | Other |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 387 | $ 880
Asset Allocation | 4.00% | 11.00%
Pension | Derivatives |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ (13) | $ (40)
Asset Allocation | 0.00% | 0.00%
Pension | Private equity funds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 465 | $ 342
Asset Allocation | 5.00% | 4.00%
Pension | Insurance-linked securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 323 | $ 186
Asset Allocation | 4.00% | 2.00%
Pension | Hedge funds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 645 | $ 774
Asset Allocation | 7.00% | 9.00%
Pension | Real estate funds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 815 | $ 584
Asset Allocation | 9.00% | 7.00%
Pension | Level 1 | Investments Excluding in Investments at NAV |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 1,890 | $ 1,492
Pension | Level 1 | Cash and short-term securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
Pension | Level 1 | Equity securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 1,903 | 1,532
Pension | Level 1 | Corporate debt securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
Pension | Level 1 | Other |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
Pension | Level 1 | Derivatives |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | (13) | (40)
Pension | Level 2 | Investments Excluding in Investments at NAV |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 4,714 | 4,841
Pension | Level 2 | Cash and short-term securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 1,493 | 1,069
Pension | Level 2 | Equity securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 162 | 828
Pension | Level 2 | Corporate debt securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 2,672 | 2,064
Pension | Level 2 | Other |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 387 | 880
Pension | Level 2 | Derivatives |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
Pension | Level 3 | Investments Excluding in Investments at NAV |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
Pension | Level 3 | Cash and short-term securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
Pension | Level 3 | Equity securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
Pension | Level 3 | Corporate debt securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
Pension | Level 3 | Other |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
Pension | Level 3 | Derivatives |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 512 | $ 457
Asset Allocation | 100.00% | 100.00%
Excluded from total investments | $ (10) | $ 1
OPEB | Cash and short-term securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 84 | $ 72
Asset Allocation | 17.00% | 16.00%
OPEB | Equity securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Asset Allocation | 55.00% | 54.00%
OPEB | Domestic |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 283 | $ 246
Asset Allocation | 55.00% | 54.00%
OPEB | Government bonds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 104 | $ 100
Asset Allocation | 20.00% | 22.00%
OPEB | Corporate debt securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 34 | $ 34
Asset Allocation | 7.00% | 7.00%
OPEB | Private equity funds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Asset Allocation | 0.00% | 0.00%
OPEB | Insurance-linked securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Asset Allocation | 0.00% | 0.00%
OPEB | Hedge funds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Asset Allocation | 0.00% | 0.00%
OPEB | Real estate funds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Asset Allocation | 0.00% | 0.00%
OPEB | Mortgage-backed securities (non-government) |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 7 | $ 5
Asset Allocation | 1.00% | 1.00%
OPEB | Level 1 |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 283 | $ 246
OPEB | Level 1 | Cash and short-term securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB | Level 1 | Domestic |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 283 | 246
OPEB | Level 1 | Government bonds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB | Level 1 | Corporate debt securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB | Level 1 | Mortgage-backed securities (non-government) |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value |  | 0
OPEB | Level 2 |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 229 | 211
OPEB | Level 2 | Cash and short-term securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 84 | 72
OPEB | Level 2 | Domestic |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB | Level 2 | Government bonds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 104 | 100
OPEB | Level 2 | Corporate debt securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 34 | 34
OPEB | Level 2 | Mortgage-backed securities (non-government) |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 7 | 5
OPEB | Level 3 |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB | Level 3 | Cash and short-term securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB | Level 3 | Domestic |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB | Level 3 | Government bonds |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB | Level 3 | Corporate debt securities |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | 0 | 0
OPEB | Level 3 | Mortgage-backed securities (non-government) |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Pension investments measured at fair value | $ 0 | $ 0

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