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, 2014		Dec. 31, 2013
Actual return on plan assets
Fair value of plan assets at end of year	$ 1,821	[1]	$ 1,769	[1]
Hedge Funds and Other Alternative Strategies Asset Position [Member]
Actual return on plan assets
Fair value of plan assets at end of year	135		110
Private Equity [Member]
Actual return on plan assets
Fair value of plan assets at end of year	84		72
Real Estate [Member]
Actual return on plan assets
Fair value of plan assets at end of year	150		133
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	237	[1]	219
Acquisitions (dispositions), net	44		(4)
Actual return on plan assets
Relating to assets sold during the reporting period	7		5
Relating to assets still held at the reporting date	16		17
Fair value of plan assets at end of year	304	[1]	237	[1]
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 [Roll Forward]
Fair value of plan assets at beginning of year	79		77
Acquisitions (dispositions), net	42		(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	126		79
Fair Value, Inputs, Level 3 [Member] | Private Equity [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	72		64
Acquisitions (dispositions), net	0		0
Actual return on plan assets
Relating to assets sold during the reporting period	5		4
Relating to assets still held at the reporting date	7		4
Fair value of plan assets at end of year	84		72
Fair Value, Inputs, Level 3 [Member] | Real Estate [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	86		78
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	6		6
Fair value of plan assets at end of year	$ 94		$ 86

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