Pension Plans and Other Postretirement Benefits (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	$ 24	$ 22	$ 49	$ 43
Interest cost	25	19	50	39
Expected return on plan assets	(26)	(23)	(53)	(46)
Amortization of net actuarial loss (gain)	8	30	17	59
Net periodic benefit cost	31	48	63	95
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	2	3	4	5
Interest cost	3	3	7	7
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss (gain)	(1)	0	(3)	0
Net periodic benefit cost	$ 4	$ 6	$ 8	$ 12