Pension and Other Postretirement Benefits - Schedule of Changes in Benefit Obligations and Plan Assets (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Change in Benefit Obligation
Benefit obligation at end of year	$ 2,100	$ 2,300
Change in Plan Assets
Fair value of plan assets at end of year	2,484	2,360
Pension Benefits [Member]
Change in Benefit Obligation
Benefit obligation at beginning of year	2,494	2,124
Service cost	53	35	35
Interest cost	100	107	107
Amendments	3
Actuarial (gain) loss	(277)	341
Benefits paid	(135)	(113)
Benefit obligation at end of year	2,238	2,494	2,124
Change in Plan Assets
Fair value of plan assets at beginning of year	2,039	1,694
Actual return on plan assets	86	252
Company and participant contributions	126	206
Benefits paid	(135)	(113)
Fair value of plan assets at end of year	2,116	2,039	1,694
Funded Status at end of year (plan assets less plan obligations)	(122)	(455)
Other Postretirement Benefits [Member]
Change in Benefit Obligation
Benefit obligation at beginning of year	775	750
Service cost	8	7	5
Interest cost	29	35	37
Amendments	(124)
Actuarial (gain) loss	(71)	24
Benefits paid	(43)	(41)
Benefit obligation at end of year	574	775	750
Change in Plan Assets
Fair value of plan assets at beginning of year	321	281
Actual return on plan assets	56	38
Company and participant contributions	34	43
Benefits paid	(43)	(41)
Fair value of plan assets at end of year	368	321	281
Funded Status at end of year (plan assets less plan obligations)	$ (206)	$ (454)