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Pensions and Other Postretirement Benefits - Narrative (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2023 USD ($) investment_firm | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan's accumulated benefit obligation | $ 2,000 | $ 1,900 |
Unfunded pension plans projected benefit obligation | 300 | 275 |
Unfunded pension plans accumulated benefit obligations | $ 273 | 249 |
Number of investment firms | investment_firm | 13 |  |
Multiemployer plan, contributions by employer | $ 11 | 13 | $ 21
Defined contribution plan, cost | 25 | 22 | $ 23
Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Trust-owned life insurance fair value | $ 138 | $ 122 |
Minimum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Pension plan assets target allocation for equity | 50.00% |  |
Maximum |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Pension plan assets target allocation for equity | 75.00% |  |
Debt securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Weighted average asset allocation, by asset category | 34.00% | 36.00% |
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Estimated net loss for defined pension plans amortized from AOCI into net periodic cost | $ 16 |  |
Assumed increases in per capita cost of covered health care benefits | 6.50% |  |
Ultimate health care cost trend rate | 5.00% |  |
Pension plan assets target allocation for equity | 75.00% |  |
Assumed rate of return on pension plan assets | 8.00% |  |
Expected contribution for the next fiscal year | $ 22 |  |
Other Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined benefit plan, future amortization of prior service cost (credit) | (26) |  |
Expected contribution for the next fiscal year | $ 31 |  |
Other Postretirement Benefits | Defined Benefit Plan, Equity Securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Weighted average asset allocation, by asset category | 66.00% | 64.00% |

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- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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