Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 42	$ 49	$ 125	$ 148
Interest cost	157	150	476	453
Expected return on plan assets	(198)	(196)	(586)	(592)
Recognized net actuarial loss	97	122	292	369
Amortization of prior service cost (benefit)	5	4	14	14
Settlement	18		18	2
Curtailment		6		6
Special termination benefits		72		72
Net periodic benefit cost	121	207	339	472
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	4	12	13
Interest cost	28	28	86	85
Recognized net actuarial loss	4	9	10	26
Amortization of prior service cost (benefit)	(6)	(4)	(15)	(13)
Net periodic benefit cost	$ 30	$ 37	$ 93	$ 111