Pension Plans, Other Postretirement Benefits, and Defined-Contribution Plans - Changes in the Fair Value of Level 3 Assets Table (Detail) (Investments [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Actual return on plan assets
Fair value of plan assets at end of year	$ 1,469	[1]	$ 1,321	[2]
Hedge Funds and Other Alternative Strategies Asset Position [Member]
Actual return on plan assets
Fair value of plan assets at end of year	97		90
Private Equity [Member]
Actual return on plan assets
Fair value of plan assets at end of year	64		55
Real Estate [Member]
Actual return on plan assets
Fair value of plan assets at end of year	124		109
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	191	[2]	99
Acquisitions (dispositions), net	15		83
Actual return on plan assets
Relating to assets still held at the reporting date	13		9
Fair value of plan assets at end of year	219	[1]	191	[2]
Fair Value, Inputs, Level 3 [Member] | Hedge Funds and Other Alternative Strategies Asset Position [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	64		49
Acquisitions (dispositions), net	9		17
Actual return on plan assets
Relating to assets sold during the reporting period	(2)		(1)
Relating to assets still held at the reporting date	6		(1)
Fair value of plan assets at end of year	77		64
Fair Value, Inputs, Level 3 [Member] | Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	55		41
Acquisitions (dispositions), net	4		6
Actual return on plan assets
Relating to assets sold during the reporting period	2		1
Relating to assets still held at the reporting date	3		7
Fair value of plan assets at end of year	64		55
Fair Value, Inputs, Level 3 [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	72		9
Acquisitions (dispositions), net	2		60
Actual return on plan assets
Relating to assets still held at the reporting date	4		3
Fair value of plan assets at end of year	$ 78		$ 72

[1] Amount excludes net receivables of $4 million, primarily related to Level 1 investments.

[2] Amount excludes net payables of $1 million, primarily related to Level 1 investments.