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Pension and Other Postretirement Benefit Plans - Fair Values of Other Postretirement Benefit Plan Assets (Details) - Other Postretirement Benefits - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 1,292	$ 1,221	$ 1,102
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	39	59
Developed markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	402	374
Emerging markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	92	101
Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1	1
Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	8
Developed markets
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	290	258
Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	275	221
Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	191	196
Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	2	3
Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	326	325
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	11	31
Level 1 | Developed markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	24	19
Level 1 | Emerging markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	16
Level 1 | Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	1	1
Level 1 | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 1 | Developed markets
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	290	258
Level 1 | Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 1 | Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 1 | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	468	428
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2 | Developed markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2 | Emerging markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2 | Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2 | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	8
Level 2 | Developed markets
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 2 | Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	275	221
Level 2 | Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	191	196
Level 2 | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	2	3
Level 3
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 3 | Developed markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 3 | Emerging markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 3 | Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 3 | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 3 | Developed markets
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 3 | Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 3 | Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
Level 3 | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
NAV
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	498	468
NAV | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	28	28
NAV | Developed markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	378	355
NAV | Emerging markets equities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	92	85
NAV | Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value		0
NAV | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
NAV | Developed markets
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
NAV | Government and agency obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
NAV | Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	0	0
NAV | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets at fair value	$ 0	$ 0

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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-Publisher FASB
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