Qualified Defined Benefit Pension Plans and Retiree Medical and Life Insurance Plans by Asset Category (Detail) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year		$ 33,204	$ 33,909
Receivables, net
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year		53	43
Investments Measured at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year		27,604	29,221
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]	2,301	2,658
Investments Measured at Fair Value | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[1]	4,166	4,790
Investments Measured at Fair Value | International equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[1]	3,971	6,121
Investments Measured at Fair Value | Commingled equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[1]	2,332	1,794
Investments Measured at Fair Value | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[1]	4,333	3,929
Investments Measured at Fair Value | U.S. Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[1]	6,811	5,069
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	[1]	919	1,377
Investments Measured at Fair Value | Other fixed income investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[1]	2,215	3,252
Investments Measured at Fair Value | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year			200
Investments Measured at Fair Value | Commodities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[1]	523	(26)
Investments Measured at Fair Value | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year		33	57
Investments Measured at Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[2]	5,547	4,645
Investments Measured at Net Asset Value | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[2]	3,614	2,931
Investments Measured at Net Asset Value | Commingled Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[2]	60	141
Investments Measured at Net Asset Value | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[2]	1,411	1,108
Investments Measured at Net Asset Value | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[2]	462	465
Fair value, inputs, level 1 | Investments Measured at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year		11,680	14,131
Fair value, inputs, 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]	2,301	2,658
Fair value, inputs, 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	[1]	4,139	4,771
Fair value, inputs, 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	[1]	3,927	6,087
Fair value, inputs, 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	[1]	788	614
Fair value, inputs, level 1 | Investments Measured at Fair Value | Commodities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[1]	525	1
Fair value, inputs, level 2 | Investments Measured at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year		15,898	14,859
Fair value, inputs, 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	[1]	23	19
Fair value, inputs, 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	[1]	40	24
Fair value, inputs, 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]	1,544	1,180
Fair value, inputs, 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	[1]	4,316	3,914
Fair value, inputs, 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	[1]	6,811	5,069
Fair value, inputs, 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	[1]	919	1,377
Fair value, inputs, 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	[1]	2,214	3,246
Fair value, inputs, level 2 | Investments Measured at Fair Value | Commodities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	[1]	(2)	(27)
Fair value, inputs, level 2 | Investments Measured at Fair Value | Hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year		33	57
Fair value, inputs, level 3 | Investments Measured at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year		26	231
Fair value, inputs, 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	[1]	4
Fair value, inputs, 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	[1]	4	10
Fair value, inputs, 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	[1]	17	15
Fair value, inputs, 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	[1]	$ 1	6
Fair value, inputs, level 3 | Investments Measured at Fair Value | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year			$ 200

[1] Cash and cash equivalents, equity securities, fixed income securities and commodities included derivative assets and liabilities whose fair values were not material as of December 31, 2016 and 2015. LMIMCo's investment policies restrict the use of derivatives to either establish long exposures for purposes of expediency or capital efficiency or to hedge risks to the extent of a plan's current exposure to such risks. Most derivative transactions are settled on a daily basis.

[2] Certain investments that are valued using the net asset value per share (or its equivalent) as a practical expedient have not been classified in the fair value hierarchy and are included in the table to permit reconciliation of the fair value hierarchy to the aggregate postretirement benefit plan assets.