Employee Benefit Plans (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated Future Employer Contributions in Current Fiscal Year	$ 46		$ 46
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated Future Employer Contributions in Current Fiscal Year	4		4
Net regulatory assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of prior service cost (credit) for regulatory assets	(2)	0	(3)	(2)
Amortization of net actuarial (gain) loss for regulatory assets	$ 1	$ 1	$ 2	$ 3