Pension Benefits (Net Periodic Pension Benefit Costs) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2011
Companies [Member] | Non-Qualified Supplemental Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-qualified supplement pension plan, funded	$ 11		$ 11
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - including administrative expenses	48	42	142	126
Interest cost on projected benefit obligation	140	139	420	417
Expected return on plan assets	(184)	(175)	(550)	(527)
Amortization of net actuarial loss	133	106	397	318
Amortization of prior service costs	2	2	6	6
NET PERIODIC BENEFIT COST	139	114	415	340
Amortization of regulatory asset			1	1
TOTAL PERIODIC BENEFIT COST	139	114	416	341
Cost capitalized	(45)	(40)	(141)	(118)
Cost deferred	(11)	(29)	(68)	(85)
Cost charged to operating expenses	83	45	207	138
Estimated future employer contributions		$ 434		$ 434	$ 533