Commitments and Contingencies (Details)	6 Months Ended
Jun. 30, 2019 USD ($) surety_bond site
Purchase Obligations
Remaining six months of 2019	$ 399,000,000
2020	658,000,000
2021	488,000,000
2022	576,000,000
2023	350,000,000
2024	228,000,000
2025 and beyond	$ 1,639,000,000
Performance Guarantees & Product Warranties [Abstract]
Number of surety bond obligations outstanding \| surety_bond	68
Performance guarantee obligations outstanding face amount	$ 705,000,000
Percentage of work yet to be completed on projects with open surety bonds	40.00%
Guarantor obligations, maximum exposure, undiscounted	$ 489,000,000
Legal, Environmental and Other Matters
Asset retirement obligation	90,000,000
Minimum [Member]
Legal, Environmental and Other Matters
Estimated capital expenditure to clean ash ponds	60,000,000
Maximum [Member]
Legal, Environmental and Other Matters
Estimated capital expenditure to clean ash ponds	80,000,000
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	$ 4,000,000
Years to resolve contingency	30 years
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
Indiana Gas Service Territory [Member]
Legal, Environmental and Other Matters
Liability recorded for environmental loss contingencies	$ 2,000,000
Environmental remediation number of sites with potential remedial responsibility \| site	26
CERC Corp [Member]
Purchase Obligations
Remaining six months of 2019	$ 276,000,000
2020	459,000,000
2021	308,000,000
2022	402,000,000
2023	197,000,000
2024	132,000,000
2025 and beyond	1,276,000,000
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	$ 4,000,000
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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Performance Guarantees & Product Warranties [Abstract]

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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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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.

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

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