Pension Plans, Other Postretirement Benefits, and Defined-Contribution Plans - Changes in the Fair Value of Level 3 Investments Table (Detail) - Investments [Member] - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year	[1]	$ 1,821
Actual return on plan assets
Fair value of plan assets at end of year	[1]	1,676		$ 1,821
Hedge Funds and Other Alternative Strategies Asset Position [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year		135
Actual return on plan assets
Fair value of plan assets at end of year		134		135
Private Equity [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year		84
Actual return on plan assets
Fair value of plan assets at end of year		92		84
Real Estate [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year		150
Actual return on plan assets
Fair value of plan assets at end of year		161		150
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year		304	[1]	237
Acquisitions (dispositions), net		(1)		44
Actual return on plan assets
Relating to assets sold during the reporting period		11		7
Relating to assets still held at the reporting date		9		16
Fair value of plan assets at end of year	[1]	323		304
Fair Value, Inputs, Level 3 [Member] | Hedge Funds and Other Alternative Strategies Asset Position [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year		126		79
Acquisitions (dispositions), net		1		42
Actual return on plan assets
Relating to assets sold during the reporting period		0		2
Relating to assets still held at the reporting date		0		3
Fair value of plan assets at end of year		127		126
Fair Value, Inputs, Level 3 [Member] | Private Equity [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year		84		72
Acquisitions (dispositions), net		(4)		0
Actual return on plan assets
Relating to assets sold during the reporting period		11		5
Relating to assets still held at the reporting date		1		7
Fair value of plan assets at end of year		92		84
Fair Value, Inputs, Level 3 [Member] | Real Estate [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Fair value of plan assets at beginning of year		94		86
Acquisitions (dispositions), net		2		2
Actual return on plan assets
Relating to assets sold during the reporting period		0		0
Relating to assets still held at the reporting date		8		6
Fair value of plan assets at end of year		$ 104		$ 94

[1] Amount excludes receivables and payables, primarily related to Level 1 investments.