Pension Plans and Other Postretirement Benefits (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 Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	$ 25	$ 21	$ 74	$ 64
Interest cost	25	19	75	58
Expected return on plan assets	(27)	(22)	(80)	(68)
Amortization of net actuarial loss (gain)	9	29	26	88
Amortization of net prior service cost (credit)	0	0	0	0
Net periodic benefit cost	32	47	95	142
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	1	2	5	7
Interest cost	4	3	11	10
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss (gain)	(2)	0	(5)	0
Amortization of net prior service cost (credit)	0	1	0	1
Net periodic benefit cost	$ 3	$ 6	$ 11	$ 18