Postretirement Benefit Plans - Qualified Defined Benefit Pension Plans and Retiree Medical and Life Insurance Plans by Asset Category (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	$ 37,361	$ 40,566
Buy-In Contract
Defined Benefit Plan Disclosure [Line Items]
Plan with benefit obligations equal to plan assets	1,500	1,700
Level 1, 2 and 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	27,446	31,500
Level 1, 2 and 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	991	1,109
Level 1, 2 and 3 | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	6,479	7,535
Level 1, 2 and 3 | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	4,882	6,844
Level 1, 2 and 3 | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	869	1,671
Level 1, 2 and 3 | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	6,397	5,732
Level 1, 2 and 3 | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	2,864	2,506
Level 1, 2 and 3 | U.S. Government-sponsored enterprise securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	228	230
Level 1, 2 and 3 | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	4,736	5,873
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	12,400	15,891
Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	991	1,109
Level 1 | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	6,444	7,467
Level 1 | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	4,880	6,836
Level 1 | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	36	442
Level 1 | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 1 | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 1 | U.S. Government-sponsored enterprise securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 1 | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	49	37
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	13,296	13,765
Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 2 | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	5	8
Level 2 | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 2 | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	833	1,228
Level 2 | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	6,295	5,730
Level 2 | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	2,864	2,506
Level 2 | U.S. Government-sponsored enterprise securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	228	230
Level 2 | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	3,071	4,063
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	1,750	1,844
Level 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 3 | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	30	60
Level 3 | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	2	8
Level 3 | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	1
Level 3 | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	102	2
Level 3 | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 3 | U.S. Government-sponsored enterprise securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 3 | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	1,616	1,773
NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	9,832	9,066
NAV | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	701	541
NAV | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	130	92
NAV | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	5,386	4,672
NAV | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	3,059	2,650
NAV | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	556	1,111
NAV | Receivables, net
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	$ 83	$ 0