Pension And OPEB (Components Of Net Periodic Benefit Cost) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 31	$ 26
Interest Cost	59	59
Expected Return on Plan Assets	(103)	(100)
Amortization of Prior Service Cost	(5)	(5)
Amortization of Actuarial Loss	37	14
Total Benefit Costs	19	(6)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	5	5
Interest Cost	17	17
Expected Return on Plan Assets	(7)	(7)
Amortization of Prior Service Cost	(3)	(4)
Amortization of Actuarial Loss	10	6
Total Benefit Costs	$ 22	$ 17