Pension, OPEB and Savings Plans (Components Of Net Periodic Benefit Cost) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 104	$ 116	$ 101
Interest Cost	234	215	223
Expected Return on Plan Assets	(399)	(348)	(306)
Amortization of Net Transition Obligation	0	0	0
Amortization of Prior Service Cost	(18)	(19)	(18)
Amortization of Actuarial Loss	56	188	167
Net Periodic Benefit Cost	(23)	152	167
Special Termination Benefits	0	0	1
Effect of Regulatory Asset	0	0	0
Total Benefit Costs, Including Effect of Regulatory Asset	(23)	152	168
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	18	21	17
Interest Cost	69	63	65
Expected Return on Plan Assets	(26)	(21)	(17)
Amortization of Net Transition Obligation	0	0	2
Amortization of Prior Service Cost	(14)	(14)	(14)
Amortization of Actuarial Loss	23	42	31
Net Periodic Benefit Cost	70	91	84
Special Termination Benefits	0
Effect of Regulatory Asset	0	0	19
Total Benefit Costs, Including Effect of Regulatory Asset	$ 70	$ 91	$ 103