Defined benefit plan estimated funded percent.

No definition available.

Name:	te_DefinedBenefitPlanEstimatedFundedPercent
Namespace Prefix:	te_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Defined benefit plan estimated future employer contributions in years two through five.

+ References

No definition available.

+ Details

Name:	te_DefinedBenefitPlanEstimatedFutureEmployerContributionsInYearsTwoThroughFive
Namespace Prefix:	te_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Defined benefit plan net loss that will be amortized from regulatory assets in next fiscal year.

+ References

No definition available.

+ Details

Name:	te_DefinedBenefitPlanNetLossThatWillBeAmortizedFromRegulatoryAssetsInNextFiscalYear
Namespace Prefix:	te_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Defined contribution plan employer discretionary matching contribution percent of match.

+ References

No definition available.

+ Details

Name:	te_DefinedContributionPlanEmployerDiscretionaryMatchingContributionPercentOfMatch
Namespace Prefix:	te_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Effective date of employer matching contribution increase

+ References

No definition available.

+ Details

Name:	te_EffectiveDateOfEmployerMatchingContributionIncrease
Namespace Prefix:	te_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Other postretirement benefit plans service benefit that will be amortized from regulatory assets in next fiscal year

+ References

No definition available.

+ Details

Name:	te_OtherPostretirementBenefitPlansServiceBenefitThatWillBeAmortizedFromRegulatoryAssetsInNextFiscalYear
Namespace Prefix:	te_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of defined benefit plan assets decreased.

+ References

No definition available.

+ Details

Name:	te_PercentageOfDefinedBenefitPlanAssetsDecreased
Namespace Prefix:	te_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of tax free subsidy under prescription drug programs.

+ References

No definition available.

+ Details

Name:	te_PercentageOfTaxFreeSubsidyUnderPrescriptionDrugPrograms
Namespace Prefix:	te_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Pre acquisition regulated asset that will be amortized from regulatory assets in next fiscal year.

+ References

No definition available.

+ Details

Name:	te_PreAcquisitionRegulatedAssetThatWillBeAmortizedFromRegulatoryAssetsInNextFiscalYear
Namespace Prefix:	te_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Tax of premiums paid for retiree medical benefits plan.

+ References

No definition available.

+ Details

Name:	te_TaxOfPremiumsPaidForRetireeMedicalBenefitsPlan
Namespace Prefix:	te_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Accumulated Benefit Obligation
-URI http://asc.fasb.org/extlink&oid=6503844

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

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

- Definition

This represents the entire assets recognized in the balance sheet that are associated with the defined benefit plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.10)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=21915240&loc=d3e1703-114919

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsCurrentAndNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The increase in the fair value of plan assets from contributions made by the employer.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 30
-Section 35
-Paragraph 50
-URI http://asc.fasb.org/extlink&oid=49178875&loc=d3e12355-114930

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Plan assets of a defined benefit plan, as a percentage of projected benefit obligation.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlanFundedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount included in accumulated other comprehensive income (AOCI) related to prior service cost (credit) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

+ References

+ Details

Name:	us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of the terms and benefits provided by the employer's defined contribution plans. A defined contribution plan provides benefits in return for services rendered, provides an individual account for each participant, and has terms that specify how contributions to the individual's account are to be determined rather than the amount of benefits the individual is to receive. Under a defined contribution pension plan, the benefits a participant will receive depend solely on the amount contributed to the participant's account, the returns earned on investments of those contributions, and forfeitures of other participants' benefits that may be allocated to such participant's account. A description of the plan(s) including employee groups covered, the basis for determining contributions, and the nature and effects of significant matters affecting comparability of information for all periods presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Defined Contribution Plan
-URI http://asc.fasb.org/extlink&oid=49180617

+ Details

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

- Definition

Description of and general information regarding the types of plans utilized by the employer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2410-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2417-114920

+ Details

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

- Definition

Amortization period for the recovery of regulatory asset, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_RegulatoryAssetAmortizationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementScenarioAxis=te_PreAmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=te_PostAmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=te_UnqualifiedSupplementalEmployeeRetirementPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_AffiliatedEntityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=te_NMGCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=te_NewMexicoGasCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Employee Postretirement Benefits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended			21 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Percentage of tax-free subsidy under prescription drug programs	28.00%
Tax of premiums paid for retiree medical benefits plan	40.00%
Accumulated benefit obligation of defined benefit pension plans	$ 686.9	$ 685.0		$ 685.0
Percentage of defined benefit plan assets decreased	3.50%
Plan assets	$ 625.4	$ 648.0		$ 648.0
Primary provisions for pension benefits	First, for plans funded less than 100%, required shortfall contributions were based on a percentage of the funding target until 2013, rather than the funding target of 100%.
Percentage of qualified pension plan's actuarial value of assets		120.10%		120.10%
Estimated percentage of qualified pension plan's actuarial value of assets	114.10%
Employer contributions	$ 55.0	$ 47.5
Employer contributions in next fiscal year	$ 37.4
Defined contribution plan, maximum employer match percentage	6.00%
Description of defined contribution plan	Employer matching contributions were 65% of eligible participant contributions with additional incentive match of up to 35% of eligible participant contributions based on the achievement of certain operating company financial goals. Prior to this, the employer matching contributions were 60% of eligible participant contributions, with an additional incentive match of up to 40%.
Defined contribution plan cost recognized	$ 11.1	13.1	$ 11.3
Employer matching contribution percentage of eligible participant contribution	70.00%
Defined benefit plan additional percentage of eligible compensation for matching contributions by employer	30.00%
Effective date of employer matching contribution increase	Jan. 01, 2015
Pre Amendment [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution percentage of eligible participant contribution	60.00%
Defined benefit plan additional percentage of eligible compensation for matching contributions by employer	40.00%
Post Amendment [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution percentage of eligible participant contribution				65.00%
Defined benefit plan additional percentage of eligible compensation for matching contributions by employer				35.00%
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Range of estimated annual contributions	$ 12.2
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Range of estimated annual contributions	44.6
Unqualified SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assets	43.5	0.9		$ 0.9
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated net loss amortization from AOCI into net periodic benefit cost related to defined benefit plan	3.5
Estimated Prior service cost amortization from AOCI into net periodic benefit cost related to defined benefit plan	0.1
Defined benefit plan net loss that will be amortized from regulatory assets in next fiscal year	9.8
Defined benefit plan, assets	208.2	167.4		167.4
Plan assets	625.4	648.0	593.0	648.0
Employer contributions	55.0	47.5
Net periodic benefit cost	22.8	25.7	29.8
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated Prior service cost amortization from AOCI into net periodic benefit cost related to defined benefit plan	0.5
Other postretirement benefit plans service benefit that will be amortized from regulatory assets in next fiscal year	2.1
Defined benefit plan, assets	32.4	26.6		26.6
Plan assets	20.6	18.8	0.0	18.8
Employer contributions	1.5	(1.0)
Employer contributions in next fiscal year	14.3
Net periodic benefit cost	6.9	12.8	12.4
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 43.4	1.2
Tampa Electric Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of tax-free subsidy under prescription drug programs	28.00%
Amortization period of Regulatory Asset	12 years
Plan assets	$ 625.4	$ 648.0		$ 648.0
Primary provisions for pension benefits	First, for plans funded less than 100%, required shortfall contributions will be based on a percentage of the funding target until 2013, rather than the funding target of 100%.
Percentage of qualified pension plan's actuarial value of assets		120.10%		120.10%
Estimated percentage of qualified pension plan's actuarial value of assets	114.10%
Employer contributions	$ 43.9	$ 38.2
Employer contributions in next fiscal year	$ 30.9
Description of defined contribution plan	Effective Jan. 1, 2015, the employer matching contributions were 70% of eligible participant contributions with additional incentive match of up to 30% of eligible participant contributions based on the achievement of certain operating company financial goals. During the period from April 2013 to December 2014, employer matching contributions were 65% of eligible participant contributions with additional incentive match of up to 35% of eligible participant contributions based on the achievement of certain operating company financial goals. Prior to this, the employer matching contributions were 60% of eligible participant contributions with additional incentive match of up to 40%.
Defined contribution plan cost recognized	$ 7.5	10.2	9.1
Employer matching contribution percentage of eligible participant contribution	70.00%
Defined benefit plan additional percentage of eligible compensation for matching contributions by employer	30.00%
Tampa Electric Company [Member] \| Pre Amendment [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution percentage of eligible participant contribution	60.00%
Defined benefit plan additional percentage of eligible compensation for matching contributions by employer	40.00%
Tampa Electric Company [Member] \| Post Amendment [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution percentage of eligible participant contribution				65.00%
Defined benefit plan additional percentage of eligible compensation for matching contributions by employer				35.00%
Tampa Electric Company [Member] \| Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Range of estimated annual contributions	$ 8.0
Tampa Electric Company [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Range of estimated annual contributions	35.0
Tampa Electric Company [Member] \| Unqualified SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assets	43.5	0.9		$ 0.9
Tampa Electric Company [Member] \| Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan net loss that will be amortized from regulatory assets in next fiscal year	9.8
Defined benefit plan, assets	208.2	167.4		167.4
Net periodic benefit cost	13.5	14.8	21.7
Tampa Electric Company [Member] \| Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Other postretirement benefit plans service benefit that will be amortized from regulatory assets in next fiscal year	1.9
Defined benefit plan, assets	30.2	20.4		20.4
Employer contributions in next fiscal year	9.3
Net periodic benefit cost	5.7	10.4	10.0
Tampa Electric Company [Member] \| SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	14.9	0.8
NMGC [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-acquisition regulated asset that will be amortized from regulatory assets in next fiscal year	1.1
NMGC [Member] \| Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions in next fiscal year	3.6
NMGC [Member] \| Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 20.6	18.8		18.8
TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of defined benefit plan assets decreased	3.50%
TECO Energy [Member] \| Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 625.4	648.0	593.0	648.0
Employer contributions	55.0	47.5
Net periodic benefit cost	22.8	25.7	29.8
TECO Energy [Member] \| Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Other postretirement benefit plans service benefit that will be amortized from regulatory assets in next fiscal year	0.0
Plan assets	20.6	18.8	0.0	$ 18.8
Employer contributions	1.5	(1.0)
Net periodic benefit cost	$ 6.9	$ 12.8	$ 12.4