Employee Benefits - Fair Values for Pension Plans by Asset Category (Detail) - Pension - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	$ 6,802	$ 13,536	$ 13,739
Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	4,146	9,104
Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	542	1,956
Fair Value, Inputs, Level 1, 2 and 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	12	69
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	720	1,412
Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	1,129	2,994
Fair Value, Inputs, Level 1, 2 and 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	113	341
Fair Value, Inputs, Level 1, 2 and 3 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	82	768
Fair Value, Inputs, Level 1, 2 and 3 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	934	996
Fair Value, Inputs, Level 1, 2 and 3 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	564	512
Fair Value, Inputs, Level 1, 2 and 3 | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	50	56
Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	1,609	3,541
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	530	1,771
Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	12	55
Level 1 | U.S. Treasuries and agencies
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	527	1,274
Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	627	204
Level 1 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	3
Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	(87)	234
Level 1 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 1 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 1 | Hedge funds
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	1,016	4,029
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	12	185
Level 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	14
Level 2 | U.S. Treasuries and agencies
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	193	138
Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	502	2,790
Level 2 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	113	338
Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	169	534
Level 2 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 2 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 2 | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	27	30
Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	1,521	1,534	1,623
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
Level 3 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	934	996	1,002
Level 3 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	564	512	569
Level 3 | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	23	26	$ 52
Investments measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	$ 2,656	$ 4,432