Postretirement Benefit Plans - Qualified Defined Benefit Pension Plans and Retiree Medical and Life Insurance Plans by Asset Category (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	$ 37,331	$ 33,646
Receivables, net
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	78	72
Investments measured at fair value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	29,459	26,442
Investments measured at fair value | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	1,961	1,727
Investments measured at fair value | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	7,189	3,936
Investments measured at fair value | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	7,244	5,406
Investments measured at fair value | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	1,933	3,587
Investments measured at fair value | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	5,208	4,890
Investments measured at fair value | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	2,260	3,399
Investments measured at fair value | U.S. Government-sponsored enterprise securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	530	571
Investments measured at fair value | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	3,134	2,926
Investments measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	7,794	7,132
Investments measured at NAV | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	32	29
Investments measured at NAV | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	181	144
Investments measured at NAV | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	4,019	4,014
Investments measured at NAV | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	2,493	2,117
Investments measured at NAV | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	1,069	828
Level 1 | Investments measured at fair value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	16,977	12,490
Level 1 | Investments measured at fair value | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	1,961	1,727
Level 1 | Investments measured at fair value | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	7,182	3,927
Level 1 | Investments measured at fair value | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	7,217	5,400
Level 1 | Investments measured at fair value | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	582	1,436
Level 1 | Investments measured at fair value | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 1 | Investments measured at fair value | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 1 | Investments measured at fair value | 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 | Investments measured at fair value | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	35	0
Level 2 | Investments measured at fair value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	11,505	13,000
Level 2 | Investments measured at fair value | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 2 | Investments measured at fair value | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	3
Level 2 | Investments measured at fair value | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	23	0
Level 2 | Investments measured at fair value | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	1,351	2,151
Level 2 | Investments measured at fair value | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	5,206	4,888
Level 2 | Investments measured at fair value | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	2,260	3,399
Level 2 | Investments measured at fair value | U.S. Government-sponsored enterprise securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	530	571
Level 2 | Investments measured at fair value | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	2,135	1,988
Level 3 | Investments measured at fair value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	977	952
Level 3 | Investments measured at fair value | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 3 | Investments measured at fair value | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	7	6
Level 3 | Investments measured at fair value | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	4	6
Level 3 | Investments measured at fair value | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 3 | Investments measured at fair value | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	2	2
Level 3 | Investments measured at fair value | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	0	0
Level 3 | Investments measured at fair value | 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 | Investments measured at fair value | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	964	938
Buy-In Contract
Defined Benefit Plan Disclosure [Line Items]
Plan with benefit obligations equal to plan assets	$ 857	$ 810