Employee 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, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Components of net periodic benefit cost:
Recognized net actuarial loss					$ (74)		$ (38)
Pension Benefits [Member]
Components of net periodic benefit cost:
Service cost	19		14		58		43
Interest cost	25		25		75		74
Expected return on plan assets	(37)		(37)		(110)		(110)
Recognized net actuarial loss	23		11		67		33
Total net periodic benefit cost	30		13		90		40
Other Benefits [Member]
Components of net periodic benefit cost:
Service cost	4		3		10		9
Interest cost	3		4		9		10
Expected return on plan assets	(4)		(4)		(10)		(10)
Amortization of transition amount	1		1		1		1
Recognized net actuarial loss	2		1		6		4
Total net periodic benefit cost	6		5		16		14
Superannuation, SERP and ESBP [Member]
Components of net periodic benefit cost:
Service cost	1	[1],[2]			1	[1],[2]	1	[1],[2]
Interest cost					2	[1],[2]	2	[1],[2]
Recognized net actuarial loss			1	[1],[2]	1	[1],[2]	1	[1],[2]
Total net periodic benefit cost	$ 1	[1],[2]	$ 1	[1],[2]	$ 4	[1],[2]	$ 4	[1],[2]

[1] Supplemental Executives Retirement Plan (SERP).

[2] Executive Supplemental Benefit Plans (ESBP).