Employee Benefits - Fair Values For Other Postretirement Benefit Plans By Asset Category (Detail) - Health Care and Life - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	$ 466	$ 450	$ 581
Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	461	441
Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	27	30
Fair Value, Inputs, Level 1, 2 and 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	229	252
Fair Value, Inputs, Level 1, 2 and 3 | U.S. Treasuries and agencies
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	138	101
Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	41	35
Fair Value, Inputs, Level 1, 2 and 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	12	12
Fair Value, Inputs, Level 1, 2 and 3 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	14	11
Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	386	369
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	1
Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	229	252
Level 1 | U.S. Treasuries and agencies
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	118	82
Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	29	25
Level 1 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	10	9
Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	75	72
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	27	29
Level 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 2 | U.S. Treasuries and agencies
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	20	19
Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	12	10
Level 2 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	2	3
Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	14	11
Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 3 | U.S. Treasuries and agencies
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 3 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 3 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Investments measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	$ 5	$ 9