Pension and Other Postretirement Benefits - Schedule of Pension Plan Benefit Obligations (Detail) - Pension Benefits [Member] - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 4,594	$ 6,904
Accumulated benefit obligation	4,438	6,702
Projected benefit obligation	3,031	6,813
Fair value of plan assets	2,579	5,267
Accumulated benefit obligation	2,918	6,210
Fair value of plan assets	$ 2,579	$ 4,805

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-Section 50
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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Amount of plan asset for defined benefit pension plan with projected benefit obligation in excess of plan assets.

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Amount of plan asset for defined benefit plan with accumulated benefit obligation in excess of plan assets.

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