Significant Accounting Policies (Components of Net Periodic Benefit Cost) (Details) (USD $) In Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Pension Benefits [Member]
Service cost for benefits earned	$ 82		$ 69		$ 164		$ 139
Interest cost	164		161		328		322
Expected return on plan assets	(167)		(156)		(334)		(312)
Amortization of transition obligation
Amortization of prior service cost	9		13		18		27
Amortization of unrecognized loss	12		11		24		21
Net periodic benefit cost	100		98		200		197
Less: transfer to regulatory account	(36)	[1]	(58)	[1]	(72)	[2]	(115)	[2]
Total	64		40		128		82
Other Benefits [Member]
Service cost for benefits earned	11		9		22		19
Interest cost	23		23		46		46
Expected return on plan assets	(20)		(18)		(40)		(36)
Amortization of transition obligation	6		6		12		12
Amortization of prior service cost	6		6		12		12
Amortization of unrecognized loss	1		1		2		2
Net periodic benefit cost	27		27		54		55
Less: transfer to regulatory account		[1]		[1]		[2]		[2]
Total	$ 27		$ 27		$ 54		$ 55

[1] The Utility recorded $36 million and $58 million for the three month periods ended June 30, 2011 and 2010, respectively, to a regulatory account as the amounts are probable of recovery from customers in future rates.

[2] The Utility recorded $72 million and $115 million for the six month periods ended June 30, 2011 and 2010, respectively, to a regulatory account as the amounts are probable of recovery from customers in future rates.