Regulatory Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets Earning a Return, Other Category		$ 16	$ 15
Regulatory Assets Earning a Return		59
Regulatory Assets Earning a Rate of Return at the Cost of Debt		34
Authorized Cost of Debt		6.065%
Regulatory Assets Earning a Rate of Return at the Cost of Capital		1
Authorized Cost of Capital		8.033%
Regulatory Assets Earning a Rate of Return by Inclusion in Rate Base		15
Regulatory Assets Earning a Rate of Return at the Approved Rate		9
Approved Rate for Deferred Account Under Amortization, Low End of Range		1.38%
Approved Rate for Deferred Accounts under Amortization, High End of Range		2.24%
Proceeds from Legal Settlements	$ 44	$ 44	$ 0	$ 0