Employee Benefits - Fair Values for Pension Plans by Asset Category (Detail) - Pension - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	$ 20,087	$ 20,128	$ 19,451
Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	13,401	13,968
Fair Value, Inputs, Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	1,221	1,968
Fair Value, Inputs, Level 1, 2 and 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	2,482	1,972
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	1,785	2,039
Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	4,046	4,110
Fair Value, Inputs, Level 1, 2 and 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	1,407	1,548
Fair Value, Inputs, Level 1, 2 and 3 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	695	916
Fair Value, Inputs, Level 1, 2 and 3 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	972	757
Fair Value, Inputs, Level 1, 2 and 3 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	569	414
Fair Value, Inputs, Level 1, 2 and 3 | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	224	244
Level 1
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	5,469	5,372
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	1,208	1,823
Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	2,463	1,623
Level 1 | U.S. Treasuries and agencies
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	1,652	1,756
Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	123	153
Level 1 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	23	17
Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	0
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	6,281	7,089
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	13	145
Level 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	19	347
Level 2 | U.S. Treasuries and agencies
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	133	283
Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	3,923	3,781
Level 2 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	1,384	1,511
Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	695	916
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	114	106
Level 3
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	1,651	1,507	1,850
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	2	3
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	176	145
Level 3 | International bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	0	20	26
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	972	757	810
Level 3 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	569	414	737
Level 3 | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	110	138	$ 129
Investments measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets amount	$ 6,686	$ 6,160