Commitments and Contingencies - Guarantees (Detail)	Sep. 30, 2016 USD ($)
Guarantee Obligations [Line Items]
Year of expiration 2016	$ 0
Year of expiration 2017	84,500,000
Year of expiration 2018-2020	0
Year of expiration After 2020	93,900,000
Maximum Theoretical Obligation	178,400,000
Liabilities Recognized at Sept. 30, 2016	0
Fuel Sales and Transportation [Member]
Guarantee Obligations [Line Items]
Year of expiration 2016	0
Year of expiration 2017	0
Year of expiration 2018-2020	0
Year of expiration After 2020	93,900,000
Maximum Theoretical Obligation	93,900,000
Liabilities Recognized at Sept. 30, 2016	0
Letters of Indemnity - Coal Mining Permits
Guarantee Obligations [Line Items]
Year of expiration 2016	0
Year of expiration 2017	84,500,000
Year of expiration 2018-2020	0
Year of expiration After 2020	0
Maximum Theoretical Obligation	84,500,000
Liabilities Recognized at Sept. 30, 2016	$ 0

Contractual obligation future minimum payments due in third through year five.

No definition available.

Name:	te_ContractualObligationFutureMinimumPaymentsDueInThirdThroughYearFive
Namespace Prefix:	te_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contractual obligation due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_ContractualObligationDueAfterFifthYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contractual obligation due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_ContractualObligationDueInSecondYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contractual obligation maturing in the remainder of the fiscal year following the latest fiscal year ended.

+ References

No definition available.

+ Details

Name:	us-gaap_ContractualObligationFutureMinimumPaymentsDueRemainderOfFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

Name:	us-gaap_GuaranteeObligationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsMaximumExposure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_GuaranteeObligationsByNatureAxis=te_FuelSalesAndTransportationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_GuaranteeObligationsByNatureAxis=te_LettersOfIndemnityCoalMiningPermitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: