Retirement Benefits and Trusteed Assets (Details 1) (Pension Plans, Defined Benefit [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 289	$ 437
Amortization of net actuarial loss	(125)	(99)
Amortization of prior service cost	(1)	(4)
Total recognized Regulatory assets and Other comprehensive income	163	334
Total recognized in net periodic pension cost, Regulatory assets and Other comprehensive income	343	480
Net actuarial loss	143	120
Prior service credit	$ 1	$ 1

Changes in Plan Assets and Benefit Obligations Recognized in Pension Cost, Comprehensive Income and Regulatory Assets

No definition available.

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- Definition

The amounts in accumulated other comprehensive income related to gains and losses that are not recognized immediately and are expected to be recognized as components of net periodic benefit cost over the next fiscal year that follows the most recent annual statement of financial position presented.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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-Paragraph 7

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-Paragraph 5

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- Definition

The amounts in accumulated other comprehensive income related to prior service cost or credit expected to be recognized as components of net periodic benefit cost over the next fiscal year that follows the most recent annual statement of financial position presented.

+ References

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- Definition

Before tax amount, net of reclassification adjustments, of the (increase) decrease in the value of the projected benefit obligation and the increase (decrease) in the value of the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption that has not been recognized in net periodic benefit cost.

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- Definition

Before tax amount, net of reclassification adjustments, of the benefit improvement costs resulting from a plan amendment that occurred that has not been recognized in net periodic benefit cost.

+ References

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 158

-Paragraph 7

-Subparagraph a

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-Topic 220

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- Definition

Before tax amount, net of reclassifications, of pension and other postretirement benefit plans (gain) loss included in accumulated other comprehensive income.

+ References

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-Name Accounting Standards Codification

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Before tax amount of the (increase) decrease in the value of the projected benefit obligation and the increase (decrease) in the value of the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption that has not been recognized in net periodic benefit cost.

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