Commitments and Contingencies (Details)	9 Months Ended
Sep. 30, 2019 USD ($) site
Purchase Obligations
Remaining three months of 2019	$ 217,000,000
2020	745,000,000
2021	614,000,000
2022	412,000,000
2023	330,000,000
2024	265,000,000
2025 and beyond	$ 1,846,000,000
Performance Guarantees & Product Warranties [Abstract]
Number of surety bond obligations outstanding	63
Performance guarantee obligations outstanding face amount	$ 627,000,000
Percentage of work yet to be completed on projects with open surety bonds	35.00%
Guarantor obligations, maximum exposure, undiscounted	$ 498,000,000
Legal, Environmental and Other Matters
Asset retirement obligation	75,000,000
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	9,000,000
Minnesota Service Territory [Member] \| Minimum [Member]
Legal, Environmental and Other Matters
Estimated remediation costs for the Minnesota sites	$ 7,000,000
Years to resolve contingency	5 years
Minnesota Service Territory [Member] \| Maximum [Member]
Legal, Environmental and Other Matters
Estimated remediation costs for the Minnesota sites	$ 51,000,000
Years to resolve contingency	50 years
Indiana Gas Service Territory [Member]
Legal, Environmental and Other Matters
Environmental remediation number of sites with potential remedial responsibility \| site	26
CERC Corp [Member]
Purchase Obligations
Remaining three months of 2019	$ 160,000,000
2020	528,000,000
2021	429,000,000
2022	235,000,000
2023	177,000,000
2024	169,000,000
2025 and beyond	1,483,000,000
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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Estimate of the reasonably possible loss exposure at an individual site.

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