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Debt and Other Obligations Debt and Other Obligations - Put and Call Options (Details) $ in Millions	12 Months Ended
	Sep. 30, 2016 USD ($) Rate_resets PARRS_issues Basis_points
Debt Instrument
Amount of redeemable bond issues outstanding	$ 411
Call price	100.00%
Bond issues with survivor's option	10
Bonds outstanding with survivor's option	$ 271
Number of issues of Putable Automatic Rate Reset Securities outstanding | PARRS_issues	2
Fixed-rate period for coupon rate reset on PARRS	5 years
Average time period	5 days
PARRS 1998 Series D Bond
Debt Instrument
Amount of redeemable bond issues outstanding	$ 274
Debt Instrument, Basis Point Spread on Variable Rate | Basis_points	94
Number of rate resets | Rate_resets	7
PARRS interest rate prior to rate reset	6.75%
PARRS interest rate after rate reset	3.55%
Amount of bonds redeemed	$ 301
PARRS 1999 Series A Bond
Debt Instrument
Amount of redeemable bond issues outstanding	$ 232
Debt Instrument, Basis Point Spread on Variable Rate | Basis_points	84
Number of rate resets | Rate_resets	6
PARRS interest rate prior to rate reset	6.50%
PARRS interest rate after rate reset	3.36%
Amount of bonds redeemed	$ 293

X

- Definition

The amount of bonds redeemed.

+ References

No definition available.

+ Details

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X

- Definition

Amount of redeemable bond issues outstanding

+ References

No definition available.

+ Details

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- Definition

Average time period

+ References

No definition available.

+ Details

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X

- Definition

The number of bond issues which include a "survivor's option" allowing for the right of redemption upon the death of a beneficial owner in certain specified circumstances.

+ References

No definition available.

+ Details

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X

- Definition

Amount of bonds outstanding which include a "survivor's option" allowing for the right of redemption upon the death of a beneficial owner in certain specified circumstances.

+ References

No definition available.

+ Details

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X

- Definition

Call price - low end of range. Shown as a percent of principal amount.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Basis points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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X

- Definition

Fixed-rate period for coupon rate reset on PARRS

+ References

No definition available.

+ Details

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X

- Definition

Number of issues of Putable Automatic Rate Reset Securities outstanding

+ References

No definition available.

+ Details

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X

- Definition

The number of times the coupon rate has been reset.

+ References

No definition available.

+ Details

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X

- Definition

The PARRS interest rate after rate reset.

+ References

No definition available.

+ Details

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Namespace Prefix:	tve_
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X

- Definition

The PARRS interest rate prior to rate reset.

+ 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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