New Accounting Standards	12 Months Ended
New Accounting Standards	Dec. 31, 2017
New Accounting Standards	2:New Accounting Standards Implementation of New Accounting Standards ASU 2017‑07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost: This standard was issued to improve the reporting of net benefit cost by employers that offer defined benefit pension plans and other postretirement benefit plans. The required effective date of the standard for CMS Energy and Consumers is January 1, 2018, but early adoption was permitted in the first interim period of 2017. CMS Energy and Consumers elected to adopt the standard as of January 1, 2017. The standard requires employers to report the service cost component of net benefit cost in the same line item on the income statement as other employee compensation costs, while presenting the other cost components separately outside of operating income. This change is to be applied retrospectively to all prior periods presented. Accordingly, for the years ended December 31, 2017, 2016, and 2015, CMS Energy and Consumers have presented the service cost component of their retirement benefits plans in maintenance and other operating expenses on the consolidated statements of income, while presenting the other components in nonoperating retirement benefits, net, under other income (expense). Prior to this standard, CMS Energy and Consumers had presented all of the cost components in maintenance and other operating expenses. Under a practical expedient permitted by the standard, CMS Energy and Consumers used benefit cost amounts disclosed for prior periods as the basis for retrospective application. In addition, under this standard, only the service cost component is eligible for capitalization as part of the cost of an asset. This change is to be applied prospectively upon adoption. Accordingly, for the year ended December 31, 2017, CMS Energy and Consumers capitalized a portion of the service cost component of their retirement benefits plans to plant, property, and equipment, while recognizing the other components in net income. In prior periods, a portion of all cost components was capitalized. For further details on the net periodic cost of CMS Energy’s and Consumers’ retirement benefits plans, see Note 12, Retirement Benefits. The implementation of this standard did not have a material impact on CMS Energy’s or Consumers’ consolidated net income, cash flows, or financial position. SEC Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act: The SEC staff issued this guidance to address situations where a registrant does not have the necessary information available, prepared, or analyzed in reasonable detail to complete the accounting for certain income tax effects of the TCJA in the period in which the TCJA was enacted. Under the guidance, registrants can report the effects of the TCJA as provisional amounts based on reasonable estimates in those areas in which the accounting is incomplete. The provisional amounts are subject to adjustment during a measurement period that can extend no longer than one year from the enactment date. For further details on how CMS Energy and Consumers applied this guidance to their consolidated financial statements, see Note 14, Income Taxes. New Accounting Standards Not Yet Effective ASU 2014‑09, Revenue from Contracts with Customers: This standard provides new guidance for recognizing revenue from contracts with customers. A primary objective of the standard is to provide a single, comprehensive revenue recognition model that will be applied across entities, industries, and capital markets. The new guidance replaces most of the existing revenue recognition requirements in GAAP, although certain guidance specific to rate-regulated utilities has been retained. The standard is effective on January 1, 2018 for CMS Energy and Consumers. Entities have the option to apply the standard retrospectively to all prior periods presented, or to apply it retrospectively only to contracts existing at the effective date, with the cumulative effect of the standard recorded as an adjustment to beginning retained earnings. CMS Energy and Consumers will apply the standard retrospectively only to contracts existing on the effective date, with the cumulative effect of the standard recorded as an adjustment to beginning retained earnings. CMS Energy and Consumers are finalizing their implementation of the standard and they do not expect it to have a material impact on their consolidated net income, cash flows, or financial position. CMS Energy and Consumers will provide additional disclosures about their revenues in accordance with the new standard, but they have not identified any significant changes in their revenue recognition practices that may be required. ASU 2016‑01, Recognition and Measurement of Financial Assets and Financial Liabilities: This standard, effective January 1, 2018 for CMS Energy and Consumers, is intended to improve the accounting for financial instruments. The standard requires investments in equity securities to be measured at fair value, with changes in fair value recognized in net income, except for certain investments such as those that qualify for equity-method accounting. The standard no longer permits unrealized gains and losses for certain equity investments to be recorded in AOCI. There are other targeted changes as well. Entities will apply the standard using a modified retrospective approach, with a cumulative adjustment recorded to beginning retained earnings on the effective date. During 2017, CMS Energy and Consumers sold the mutual fund investments in the DB SERP and reinvested in U.S. Treasury debt securities. Prior to the sale of the mutual funds, CMS Energy and Consumers recorded unrealized gains and losses on these investments in AOCI, except that unrealized losses determined to be other than temporary were reported in earnings. With the sale of these funds in 2017, CMS Energy does not expect this standard to have a significant impact on its consolidated financial statements. Consumers presently records unrealized gains and losses on its investment in CMS Energy common stock in AOCI. In accordance with the standard, as of January 1, 2018, Consumers will remove the $19 million unrealized gain and the associated deferred taxes on its investment in CMS Energy common stock from AOCI and record the gain in retained earnings. In addition, subsequent to January 1, 2018, Consumers will recognize all unrealized gains and losses on this investment in net income. The changes to the accounting treatment for this investment will be reflected in Consumers’ consolidated financial statements only, with no impact on CMS Energy’s consolidated financial statements. For further details on CMS Energy’s and Consumers’ investments in debt and equity securities, see Note 7, Financial Instruments. ASU 2016‑02, Leases: This standard establishes a new accounting model for leases. The standard will require entities to recognize lease assets and liabilities on the balance sheet for all leases with a term of more than one year, including operating leases, which are not recorded on the balance sheet under existing standards. As a result, CMS Energy and Consumers expect to recognize additional lease assets and liabilities for their operating leases under this standard. The new guidance will also amend the definition of a lease to require that a lessee control the use of a specified asset, and not simply control or take the output of the asset. On the income statement, leases that meet existing capital lease criteria will generally be accounted for under a financing model, while operating leases will generally be accounted for under a straight-line expense model. The standard will be effective on January 1, 2019 for CMS Energy and Consumers, but early adoption is permitted. As part of their adoption of the new standard, CMS Energy and Consumers expect to elect certain practical expedients permitted by the standard, under which they will not be required to perform lease assessments or reassessments for agreements existing on the effective date. CMS Energy and Consumers have decided not to adopt the standard early and are continuing to evaluate the impact of the standard on their consolidated financial statements. See Note 10, Leases and Palisades Financing, for more information on CMS Energy’s and Consumers’ operating lease obligations. ASU 2016‑13, Measurement of Credit Losses on Financial Instruments: This standard, which will be effective January 1, 2020 for CMS Energy and Consumers, provides new guidance for estimating and recording credit losses on financial instruments. The standard will apply to the recognition of loan losses at EnerBank as well as to the recognition of uncollectible accounts expense at Consumers. Entities will apply the standard using a modified retrospective approach, with a cumulative-effect adjustment recorded to beginning retained earnings on the effective date. CMS Energy and Consumers are evaluating the impact of the standard on their consolidated financial statements.
Consumers Energy Company [Member]
New Accounting Standards	2:New Accounting Standards Implementation of New Accounting Standards ASU 2017‑07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost: This standard was issued to improve the reporting of net benefit cost by employers that offer defined benefit pension plans and other postretirement benefit plans. The required effective date of the standard for CMS Energy and Consumers is January 1, 2018, but early adoption was permitted in the first interim period of 2017. CMS Energy and Consumers elected to adopt the standard as of January 1, 2017. The standard requires employers to report the service cost component of net benefit cost in the same line item on the income statement as other employee compensation costs, while presenting the other cost components separately outside of operating income. This change is to be applied retrospectively to all prior periods presented. Accordingly, for the years ended December 31, 2017, 2016, and 2015, CMS Energy and Consumers have presented the service cost component of their retirement benefits plans in maintenance and other operating expenses on the consolidated statements of income, while presenting the other components in nonoperating retirement benefits, net, under other income (expense). Prior to this standard, CMS Energy and Consumers had presented all of the cost components in maintenance and other operating expenses. Under a practical expedient permitted by the standard, CMS Energy and Consumers used benefit cost amounts disclosed for prior periods as the basis for retrospective application. In addition, under this standard, only the service cost component is eligible for capitalization as part of the cost of an asset. This change is to be applied prospectively upon adoption. Accordingly, for the year ended December 31, 2017, CMS Energy and Consumers capitalized a portion of the service cost component of their retirement benefits plans to plant, property, and equipment, while recognizing the other components in net income. In prior periods, a portion of all cost components was capitalized. For further details on the net periodic cost of CMS Energy’s and Consumers’ retirement benefits plans, see Note 12, Retirement Benefits. The implementation of this standard did not have a material impact on CMS Energy’s or Consumers’ consolidated net income, cash flows, or financial position. SEC Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act: The SEC staff issued this guidance to address situations where a registrant does not have the necessary information available, prepared, or analyzed in reasonable detail to complete the accounting for certain income tax effects of the TCJA in the period in which the TCJA was enacted. Under the guidance, registrants can report the effects of the TCJA as provisional amounts based on reasonable estimates in those areas in which the accounting is incomplete. The provisional amounts are subject to adjustment during a measurement period that can extend no longer than one year from the enactment date. For further details on how CMS Energy and Consumers applied this guidance to their consolidated financial statements, see Note 14, Income Taxes. New Accounting Standards Not Yet Effective ASU 2014‑09, Revenue from Contracts with Customers: This standard provides new guidance for recognizing revenue from contracts with customers. A primary objective of the standard is to provide a single, comprehensive revenue recognition model that will be applied across entities, industries, and capital markets. The new guidance replaces most of the existing revenue recognition requirements in GAAP, although certain guidance specific to rate-regulated utilities has been retained. The standard is effective on January 1, 2018 for CMS Energy and Consumers. Entities have the option to apply the standard retrospectively to all prior periods presented, or to apply it retrospectively only to contracts existing at the effective date, with the cumulative effect of the standard recorded as an adjustment to beginning retained earnings. CMS Energy and Consumers will apply the standard retrospectively only to contracts existing on the effective date, with the cumulative effect of the standard recorded as an adjustment to beginning retained earnings. CMS Energy and Consumers are finalizing their implementation of the standard and they do not expect it to have a material impact on their consolidated net income, cash flows, or financial position. CMS Energy and Consumers will provide additional disclosures about their revenues in accordance with the new standard, but they have not identified any significant changes in their revenue recognition practices that may be required. ASU 2016‑01, Recognition and Measurement of Financial Assets and Financial Liabilities: This standard, effective January 1, 2018 for CMS Energy and Consumers, is intended to improve the accounting for financial instruments. The standard requires investments in equity securities to be measured at fair value, with changes in fair value recognized in net income, except for certain investments such as those that qualify for equity-method accounting. The standard no longer permits unrealized gains and losses for certain equity investments to be recorded in AOCI. There are other targeted changes as well. Entities will apply the standard using a modified retrospective approach, with a cumulative adjustment recorded to beginning retained earnings on the effective date. During 2017, CMS Energy and Consumers sold the mutual fund investments in the DB SERP and reinvested in U.S. Treasury debt securities. Prior to the sale of the mutual funds, CMS Energy and Consumers recorded unrealized gains and losses on these investments in AOCI, except that unrealized losses determined to be other than temporary were reported in earnings. With the sale of these funds in 2017, CMS Energy does not expect this standard to have a significant impact on its consolidated financial statements. Consumers presently records unrealized gains and losses on its investment in CMS Energy common stock in AOCI. In accordance with the standard, as of January 1, 2018, Consumers will remove the $19 million unrealized gain and the associated deferred taxes on its investment in CMS Energy common stock from AOCI and record the gain in retained earnings. In addition, subsequent to January 1, 2018, Consumers will recognize all unrealized gains and losses on this investment in net income. The changes to the accounting treatment for this investment will be reflected in Consumers’ consolidated financial statements only, with no impact on CMS Energy’s consolidated financial statements. For further details on CMS Energy’s and Consumers’ investments in debt and equity securities, see Note 7, Financial Instruments. ASU 2016‑02, Leases: This standard establishes a new accounting model for leases. The standard will require entities to recognize lease assets and liabilities on the balance sheet for all leases with a term of more than one year, including operating leases, which are not recorded on the balance sheet under existing standards. As a result, CMS Energy and Consumers expect to recognize additional lease assets and liabilities for their operating leases under this standard. The new guidance will also amend the definition of a lease to require that a lessee control the use of a specified asset, and not simply control or take the output of the asset. On the income statement, leases that meet existing capital lease criteria will generally be accounted for under a financing model, while operating leases will generally be accounted for under a straight-line expense model. The standard will be effective on January 1, 2019 for CMS Energy and Consumers, but early adoption is permitted. As part of their adoption of the new standard, CMS Energy and Consumers expect to elect certain practical expedients permitted by the standard, under which they will not be required to perform lease assessments or reassessments for agreements existing on the effective date. CMS Energy and Consumers have decided not to adopt the standard early and are continuing to evaluate the impact of the standard on their consolidated financial statements. See Note 10, Leases and Palisades Financing, for more information on CMS Energy’s and Consumers’ operating lease obligations. ASU 2016‑13, Measurement of Credit Losses on Financial Instruments: This standard, which will be effective January 1, 2020 for CMS Energy and Consumers, provides new guidance for estimating and recording credit losses on financial instruments. The standard will apply to the recognition of loan losses at EnerBank as well as to the recognition of uncollectible accounts expense at Consumers. Entities will apply the standard using a modified retrospective approach, with a cumulative-effect adjustment recorded to beginning retained earnings on the effective date. CMS Energy and Consumers are evaluating the impact of the standard on their consolidated financial statements.