Employee Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 22	$ 18
Interest cost	25	26
Expected return on plan assets	(41)	(37)
Recognized net actuarial loss	27	23
Total net periodic benefit cost	33	30
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	3
Interest cost	3	3
Expected return on plan assets	(4)	(3)
Recognized net actuarial loss	1	2
Total net periodic benefit cost	4	5
Superannuation, SERP and ESBP [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1
Recognized net actuarial loss	1	1
Total net periodic benefit cost	$ 2	$ 2