Basis of Presentation (Details) shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2016 USD ($) mi² retail_customers shares	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Basis of Presentation [Abstract]
Regulatory deferral of settled derivative instruments		$ 2
Service Area Sq Miles \| mi²	4,000
Incorporated Cities	52
Number of Retail Customers \| retail_customers	855,573
Service Area Population \| shares	1.8
Percent of State's Population	46.00%
Other Comprehensive Income	$ 0	0
Unamortized Debt Issuance Expense	$ 12		$ 11
Decoupling Mechanism Deferrals, Net		(3)
Cash received pursuant to the Residential Exchange Program		$ 1

Basis of Presentation [Abstract]

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- Definition

The deferral, which can be either a positive or negaitive amount depending on whether a collection from or refund to customers results, of the amounts recorded in net income for energy useage by customers on a weather adjusted basis that is different from base rates as determined under the Company's decoupling mechanism, expected to be recovered or refunded in future periods.

+ References

No definition available.

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- Definition

Number of incorporated cities in service area.

+ References

No definition available.

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- Definition

Includes residential, commercial and industrial.

+ References

No definition available.

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- Definition

Service area population as a percent of the state's population.

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- Definition

Service Area Population

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Approximate square miles of service area.

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No definition available.

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- Definition

Gain (loss) related to the termination of a contract between the parties. The termination may be due to many causes including early termination of a lease by a lessee, a breach of contract by one party, or a failure to perform.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
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The increase (decrease) during the reporting period in the amount of (a) prepayments by customers for goods or services to be provided at a later date, (b) the amount of customer money held in customer accounts, including security deposits, collateral for a current or future transactions, initial payment of the cost of acquisition or for the right to enter into a contract or agreement, or (c) a combination of (a) and (b).

+ References

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- Definition

Amount after tax of other comprehensive income (loss) attributable to parent entity.

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

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-Name Accounting Standards Codification
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-Section S99
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