Employee Benefits - Fair Values For Other Postretirement Benefit Plans By Asset Category (Detail) - Health Care and Life - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	$ 581	$ 572	$ 743
Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	568	364
Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	36	40
Fair Value, Inputs, Level 1, 2 and 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	284	178
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	160	83
Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	64	54
Fair Value, Inputs, Level 1, 2 and 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	14	9
Fair Value, Inputs, Level 1, 2 and 3 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	10
Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	494	324
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	284	178
Level 1 | U.S. Treasuries and agencies
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	150	83
Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	50	54
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
Level 2
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	74	40
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	36	40
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	10	0
Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	14	0
Level 2 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	4	0
Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	10
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
Investments measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	$ 13	$ 208