New Accounting Standards	12 Months Ended
New Accounting Standards	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Standards	New Accounting Standards Implementation of New Accounting Standards ASU 2014-09, Revenue from Contracts with Customers: This standard, which was effective on January 1, 2018 for CMS Energy and Consumers, 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 replaced most of the previous revenue recognition requirements in GAAP, although certain guidance specific to rate-regulated utilities was retained. CMS Energy and Consumers had the option to apply the standard retrospectively to all prior periods presented or retrospectively with the cumulative effect of the standard recorded as an adjustment to beginning retained earnings. They also had the option to apply the standard only to contracts existing on the effective date. CMS Energy and Consumers applied the standard retrospectively to contracts existing on the effective date, and recorded an immaterial cumulative-effect reduction to beginning retained earnings for certain contract costs that can no longer be deferred under the new guidance. 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. CMS Energy and Consumers did not identify any significant changes to their revenue recognition practices that were required by the new guidance, but in accordance with the standard, they have provided additional disclosures about their revenues in Note 16, Revenue. ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities: This standard, which was effective on 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 must apply the standard using a modified retrospective approach, with the cumulative effect of the standard recorded as an adjustment to beginning retained earnings. The implementation of the standard had no impact on CMS Energy’s consolidated financial statements. In accordance with the standard, as of January 1, 2018, Consumers removed a $19 million unrealized gain and the associated deferred taxes on its investment in CMS Energy common stock from AOCI and recorded the gain in retained earnings. In January 2018, Consumers transferred substantially all of its shares in CMS Energy common stock to a related charitable foundation and, in accordance with this standard, recognized all unrealized gains and losses on its remaining shares in net income for the year ended December 31, 2018. The accounting treatment for this investment is reflected in Consumers’ consolidated financial statements only, and had 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 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income: This standard addresses the income tax effects stranded in AOCI as a result of the TCJA. Existing GAAP requires that the remeasurement of deferred tax assets and liabilities resulting from a change in tax laws or rates be presented in net income from continuing operations, even if the deferred taxes were associated with items that were originally recognized in AOCI. As a result, upon recognizing the effects of the TCJA, the tax effects of items in AOCI (referred to as stranded tax effects) no longer reflected the current income tax rate. To address this matter, this standard permits companies to reclassify to retained earnings the stranded tax effects of the TCJA. The standard is effective on January 1, 2019 for CMS Energy and Consumers, but early adoption is permitted. The new guidance is to be applied either in the period of adoption or retrospectively to each prior period in which the effect of the TCJA was recognized. CMS Energy and Consumers elected to adopt this standard early. Accordingly, as of January 1, 2018, CMS Energy reclassified $11 million of stranded tax effects from AOCI to retained earnings, which included $5 million reclassified at Consumers. At December 31, 2018, CMS Energy and Consumers did not have any material stranded tax effects remaining in AOCI. New Accounting Standards Not Yet Effective ASU 2016-02, Leases: This standard establishes a new accounting model for leases. The standard requires 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. The new guidance also amends 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 statement of income, 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 is effective on January 1, 2019 for CMS Energy and Consumers, but early adoption is permitted. CMS Energy and Consumers did not adopt the standard early and will 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. They also will elect a transition method under which they will initially apply the standard on January 1, 2019, without adjusting amounts presented for prior periods. Under this method, the cumulative effect of applying the standard must be recorded as an adjustment to beginning retained earnings. Under the standard, CMS Energy and Consumers will recognize additional lease assets and liabilities on their consolidated balance sheets as of January 1, 2019 for their operating leases. CMS Energy and Consumers are finalizing their implementation of the standard and do not expect it to have a material impact on their consolidated net income or cash flows. 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
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Standards	New Accounting Standards Implementation of New Accounting Standards ASU 2014-09, Revenue from Contracts with Customers: This standard, which was effective on January 1, 2018 for CMS Energy and Consumers, 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 replaced most of the previous revenue recognition requirements in GAAP, although certain guidance specific to rate-regulated utilities was retained. CMS Energy and Consumers had the option to apply the standard retrospectively to all prior periods presented or retrospectively with the cumulative effect of the standard recorded as an adjustment to beginning retained earnings. They also had the option to apply the standard only to contracts existing on the effective date. CMS Energy and Consumers applied the standard retrospectively to contracts existing on the effective date, and recorded an immaterial cumulative-effect reduction to beginning retained earnings for certain contract costs that can no longer be deferred under the new guidance. 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. CMS Energy and Consumers did not identify any significant changes to their revenue recognition practices that were required by the new guidance, but in accordance with the standard, they have provided additional disclosures about their revenues in Note 16, Revenue. ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities: This standard, which was effective on 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 must apply the standard using a modified retrospective approach, with the cumulative effect of the standard recorded as an adjustment to beginning retained earnings. The implementation of the standard had no impact on CMS Energy’s consolidated financial statements. In accordance with the standard, as of January 1, 2018, Consumers removed a $19 million unrealized gain and the associated deferred taxes on its investment in CMS Energy common stock from AOCI and recorded the gain in retained earnings. In January 2018, Consumers transferred substantially all of its shares in CMS Energy common stock to a related charitable foundation and, in accordance with this standard, recognized all unrealized gains and losses on its remaining shares in net income for the year ended December 31, 2018. The accounting treatment for this investment is reflected in Consumers’ consolidated financial statements only, and had 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 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income: This standard addresses the income tax effects stranded in AOCI as a result of the TCJA. Existing GAAP requires that the remeasurement of deferred tax assets and liabilities resulting from a change in tax laws or rates be presented in net income from continuing operations, even if the deferred taxes were associated with items that were originally recognized in AOCI. As a result, upon recognizing the effects of the TCJA, the tax effects of items in AOCI (referred to as stranded tax effects) no longer reflected the current income tax rate. To address this matter, this standard permits companies to reclassify to retained earnings the stranded tax effects of the TCJA. The standard is effective on January 1, 2019 for CMS Energy and Consumers, but early adoption is permitted. The new guidance is to be applied either in the period of adoption or retrospectively to each prior period in which the effect of the TCJA was recognized. CMS Energy and Consumers elected to adopt this standard early. Accordingly, as of January 1, 2018, CMS Energy reclassified $11 million of stranded tax effects from AOCI to retained earnings, which included $5 million reclassified at Consumers. At December 31, 2018, CMS Energy and Consumers did not have any material stranded tax effects remaining in AOCI. New Accounting Standards Not Yet Effective ASU 2016-02, Leases: This standard establishes a new accounting model for leases. The standard requires 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. The new guidance also amends 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 statement of income, 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 is effective on January 1, 2019 for CMS Energy and Consumers, but early adoption is permitted. CMS Energy and Consumers did not adopt the standard early and will 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. They also will elect a transition method under which they will initially apply the standard on January 1, 2019, without adjusting amounts presented for prior periods. Under this method, the cumulative effect of applying the standard must be recorded as an adjustment to beginning retained earnings. Under the standard, CMS Energy and Consumers will recognize additional lease assets and liabilities on their consolidated balance sheets as of January 1, 2019 for their operating leases. CMS Energy and Consumers are finalizing their implementation of the standard and do not expect it to have a material impact on their consolidated net income or cash flows. 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.