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	$ 13	$ 11
Interest cost	25	26
Expected return on plan assets	(37)	(34)
Amortization of net actuarial loss	16	14
Net periodic benefit cost	17	17
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	1
Interest cost	8	9
Expected return on plan assets	(5)	(5)
Amortization of prior service cost	(1)	(1)
Amortization of net actuarial loss	4	5
Net periodic benefit cost	$ 8	$ 9