Regulatory Matters (Details Textuals) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Jun. 30, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Regulatory Asset and Liability [Line Items]
Requested net recovery of RETM and LCT		$ 44
Period to Recover Surcharges for RETM and LCT	3 months
Requesting Authority to Refund Uncollectible Expense to Customers		9
Time Period to Refund UETM Overrecovery	1 month
Net Under Recovery of Power Suppy Cost Recovery Expense			$ 87	$ 148