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
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 8	$ 10	$ 26	$ 27
Interest cost	27	27	80	80
Expected return on plan assets	(33)	(32)	(99)	(96)
Amortization of prior service cost (benefit)	1		2	(1)
Amortization of net actuarial loss	16	11	48	35
Net periodic benefit cost	19	16	57	45
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	1	6	4
Interest cost	9	10	26	28
Expected return on plan assets	(5)	(5)	(14)	(14)
Amortization of prior service cost (benefit)	(1)	(1)	(3)	(3)
Amortization of net actuarial loss	4	3	11	9
Termination benefits			1	1
Net periodic benefit cost	$ 9	$ 8	$ 27	$ 25