Commitments and Contingencies - Schedule of Long-term Commitments (Detail) $ in Millions	Mar. 31, 2022 USD ($)
Other Commitments [Line Items]
2022	$ 829
2023	358
2024	248
2025	223
2026	217
Thereafter	1,968
Total future minimum payments	3,843
Transportation [Member]
Other Commitments [Line Items]
2022	182
2023	224
2024	215
2025	200
2026	197
Thereafter	1,868
Total future minimum payments	2,886
Capital Projects [Member]
Other Commitments [Line Items]
2022	224
2023	63
2024	2
2025	1
2026	0
Thereafter	0
Total future minimum payments	290
Fuel and Gas Supply [Member]
Other Commitments [Line Items]
2022	393
2023	38
2024	0
2025	0
2026	0
Thereafter	0
Total future minimum payments	431
Long-term Service Agreements [Member]
Other Commitments [Line Items]
2022	24
2023	29
2024	27
2025	19
2026	19
Thereafter	52
Total future minimum payments	170
Operating Leases [Member]
Other Commitments [Line Items]
2022	2
2023	3
2024	3
2025	2
2026	1
Thereafter	48
Total future minimum payments	59
Demand Side Management [Member]
Other Commitments [Line Items]
2022	4
2023	1
2024	1
2025	1
2026	0
Thereafter	0
Total future minimum payments	$ 7

Contractual obligation due after fourth year.

No definition available.

Name:	ck0000096271_ContractualObligationDueAfterFourthYear
Namespace Prefix:	ck0000096271_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

+ References

No definition available.

+ Details

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

- Definition

Amount of contractual obligation to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

No definition available.

+ Details

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

- Definition

Amount of contractual obligation to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

No definition available.

+ Details

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

- Definition

Amount of contractual obligation to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ 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 to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

No definition available.

+ Details

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

- Definition

Amount of contractual obligation to be paid in remainder of current fiscal year.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_TypeOfArrangementAxis=ck0000096271_TransportationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ck0000096271_CapitalProjectsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ck0000096271_FuelAndGasSupplyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ck0000096271_LongTermServiceAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ck0000096271_OperatingLeasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=ck0000096271_DemandSideManagementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: