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Benefit Plans Expected Amortization of Regulatory Assets in Next Fiscal Year (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Pension Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Other Costs		$ (228)	$ 0	$ 0
Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Other Costs		$ 0	$ 0	$ 0
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure
Prior service cost (credit)	$ (29)
Net actuarial loss	299
Scenario, Forecast [Member] | Pension Benefits
Defined Benefit Plan Disclosure
Defined Benefit Plan, Other Costs	231
Prior service cost (credit)	(23)
Net actuarial loss	291
Scenario, Forecast [Member] | Other Post-retirement Benefits
Defined Benefit Plan Disclosure
Prior service cost (credit)	(6)
Net actuarial loss	$ 8

X

- Definition

The amounts in regulatory assets 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

No definition available.

+ Details

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Period Type:	duration

X

- Definition

The amounts in regulatory assets 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

No definition available.

+ Details

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X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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X

- Definition

Amount of other defined benefit plan costs.

+ References

No definition available.

+ Details

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- Details

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