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Employee Benefit Plans (Significant Unobservable Inputs) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
Pension Benefits |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | $ 8,294 | $ 10,971
Purchases, sales, issuances and settlements, net | (35) | (38)
Estimated fair value of plan assets at December 31, | 8,270 | 8,294
Pension Benefits | Foreign government |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 769 |
Estimated fair value of plan assets at December 31, | 810 | 769
Pension Benefits | Other (1) |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 693 |
Estimated fair value of plan assets at December 31, | 699 | 693
Pension Benefits | Equity Securities |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 570 |
Estimated fair value of plan assets at December 31, | 610 | 570
Pension Benefits | Corporate fixed maturity securities |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 3,001 |
Estimated fair value of plan assets at December 31, | 3,083 | 3,001
Other Postretirement Benefits |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 1,303 | 1,443
Purchases, sales, issuances and settlements, net | 0 | 0
Estimated fair value of plan assets at December 31, | 1,334 | 1,303
Other Postretirement Benefits | Foreign government |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 61 |
Estimated fair value of plan assets at December 31, | 46 | 61
Other Postretirement Benefits | Other (1) |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 44 |
Estimated fair value of plan assets at December 31, | 37 | 44
Other Postretirement Benefits | Equity Securities |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 47 |
Estimated fair value of plan assets at December 31, | 59 | 47
Other Postretirement Benefits | Corporate fixed maturity securities |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 205 |
Estimated fair value of plan assets at December 31, | 167 | 205
Level 3 | Pension Benefits |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 920 |
Estimated fair value of plan assets at December 31, | 904 | 920
Level 3 | Pension Benefits | Foreign government |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 0 | 1
Realized gains (losses) | 0 | 0
Unrealized gains (losses) | 0 | 0
Purchases, sales, issuances and settlements, net | 0 | 0
Transfers into and/or out of Level 3 | 2 | (1)
Estimated fair value of plan assets at December 31, | 2 | 0
Level 3 | Pension Benefits | Other (1) |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 3 | 1
Realized gains (losses) | 0 | 0
Unrealized gains (losses) | 0 | 0
Purchases, sales, issuances and settlements, net | 0 | 3
Transfers into and/or out of Level 3 | 5 | (1)
Estimated fair value of plan assets at December 31, | 8 | 3
Level 3 | Pension Benefits | Equity Securities |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 3 | 11
Realized gains (losses) | 0 | 0
Unrealized gains (losses) | 1 | 0
Purchases, sales, issuances and settlements, net | 8 | (8)
Transfers into and/or out of Level 3 | 0 | 0
Estimated fair value of plan assets at December 31, | 12 | 3
Level 3 | Pension Benefits | Other investments |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 855 | 954
Realized gains (losses) | (1) | 0
Unrealized gains (losses) | (51) | 54
Purchases, sales, issuances and settlements, net | 25 | (153)
Transfers into and/or out of Level 3 | 0 | 0
Estimated fair value of plan assets at December 31, | 828 | 855
Level 3 | Pension Benefits | Corporate fixed maturity securities |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 55 | 0
Realized gains (losses) | 0 | 0
Unrealized gains (losses) | 1 | (1)
Purchases, sales, issuances and settlements, net | 2 | 56
Transfers into and/or out of Level 3 | (4) | 0
Estimated fair value of plan assets at December 31, | 54 | 55
Level 3 | Pension Benefits | Derivative Financial Instruments, Assets |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 4 | 0
Realized gains (losses) | 0 | 0
Unrealized gains (losses) | (1) | 1
Purchases, sales, issuances and settlements, net | (3) | 3
Transfers into and/or out of Level 3 | 0 | 0
Estimated fair value of plan assets at December 31, | 0 | 4
Level 3 | Other Postretirement Benefits |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 0 |
Estimated fair value of plan assets at December 31, | 0 | 0
Level 3 | Other Postretirement Benefits | Foreign government |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 0 |
Estimated fair value of plan assets at December 31, | 0 | 0
Level 3 | Other Postretirement Benefits | Other (1) |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 0 |
Estimated fair value of plan assets at December 31, | 0 | 0
Level 3 | Other Postretirement Benefits | Equity Securities |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 0 |
Estimated fair value of plan assets at December 31, | 0 | 0
Level 3 | Other Postretirement Benefits | Corporate fixed maturity securities |  |
Rollforward fair value measurement using significant unobservable inputs (level 3) [Roll Forward] |  |
Estimated fair value of plan assets at January 1, | 0 |
Estimated fair value of plan assets at December 31, | $ 0 | $ 0

X
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- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(A) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(B) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan, for assets transferred into (out of) Level 3 of fair value hierarchy. Includes, but is not limited to, transfer due to change in observability of significant inputs. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(C) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
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