Commitments and Contingencies (Details)	3 Months Ended
Mar. 31, 2019 USD ($) surety_bond site
Purchase Obligations
Remaining nine months of 2019	$ 427,000,000
2020	620,000,000
2021	531,000,000
2022	406,000,000
2023	308,000,000
2024	328,000,000
2025 and beyond	$ 1,445,000,000
Performance Guarantees & Product Warranties [Abstract]
Number of surety bond obligations outstanding \| surety_bond	63
Performance guarantee obligations outstanding face amount	$ 600,000,000
Percentage of work yet to be completed on projects with open surety bonds	35.00%
Guarantor obligations, maximum exposure, undiscounted	$ 473,000,000
Legal, Environmental and Other Matters
Asset retirement obligation	46,000,000
Minimum [Member]
Legal, Environmental and Other Matters
Estimated capital expenditure to clean ash ponds	45,000,000
Maximum [Member]
Legal, Environmental and Other Matters
Estimated capital expenditure to clean ash ponds	65,000,000
Minnesota Service Territory [Member]
Legal, Environmental and Other Matters
Liability recorded for environmental loss contingencies	7,000,000
Minnesota Service Territory [Member] \| Minimum [Member]
Legal, Environmental and Other Matters
Estimated remediation costs for the Minnesota sites	$ 5,000,000
Years to resolve contingency	30
Minnesota Service Territory [Member] \| Maximum [Member]
Legal, Environmental and Other Matters
Estimated remediation costs for the Minnesota sites	$ 32,000,000
Years to resolve contingency	50
Indiana Gas Service Territory [Member]
Legal, Environmental and Other Matters
Liability recorded for environmental loss contingencies	$ 3,000,000
Environmental remediation number of sites with potential remedial responsibility \| site	26
CERC Corp [Member]
Purchase Obligations
Remaining nine months of 2019	$ 282,000,000
2020	420,000,000
2021	351,000,000
2022	232,000,000
2023	155,000,000
2024	231,000,000
2025 and beyond	1,083,000,000
CERC Corp [Member] \| Minnesota Service Territory [Member]
Legal, Environmental and Other Matters
Liability recorded for environmental loss contingencies	7,000,000
CERC Corp [Member] \| Minnesota Service Territory [Member] \| Minimum [Member]
Legal, Environmental and Other Matters
Estimated remediation costs for the Minnesota sites	$ 5,000,000
Years to resolve contingency	30 years
CERC Corp [Member] \| Minnesota Service Territory [Member] \| Maximum [Member]
Legal, Environmental and Other Matters
Estimated remediation costs for the Minnesota sites	$ 32,000,000
Years to resolve contingency	50 years
Minnehaha Academy Gas Explosion [Member]
Legal, Environmental and Other Matters
Contested amount of fines imposed	$ 200,000
Minnehaha Academy Gas Explosion [Member] \| CERC Corp [Member]
Legal, Environmental and Other Matters
Contested amount of fines imposed	$ 200,000

Contested amount of fines imposed by the Minnesota Office of Pipeline Safety.

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Number of sites identified where the entity may potentially have some remedial responsibility

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Estimated Capital Expenditure to Clean Ash Ponds

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Percentage of work yet to be completed by wholly owned subsidiary on projects with open surety bonds.

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Face amount of individual surety bonds the wholly-owned subsidiary has outstanding

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Estimate of the reasonably possible loss exposure at an individual site.

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Minimum amount of purchase arrangement maturing after the fifth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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