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Financings and Capitalization (Major Long-Term Debt Transactions) (Details) - USD ($) $ in Millions | 1 Months Ended | 9 Months Ended
--- | --- | ---
Oct. 31, 2019 | Sep. 30, 2019
Debt Instrument [Line Items] |  |
Principal balance |  | $ 2,021
Debt retirement, principal |  | 845
Consumers Energy Company |  |
Debt Instrument [Line Items] |  |
Principal balance |  | 926
Debt retirement, principal |  | 300
First mortgage bonds due February 2050 | Consumers Energy Company |  |
Debt Instrument [Line Items] |  |
Principal balance |  | $ 300
Interest Rate |  | 3.75%
Debt issuance date |  | May 2019
Maturity Date |  | February 2050
First Mortgage Bonds Due August 2050 | Consumers Energy Company |  |
Debt Instrument [Line Items] |  |
Principal balance |  | $ 550
Interest Rate |  | 3.10%
Debt issuance date |  | September 2019
Maturity Date |  | August 2050
Floating First Rate Mortgage Bonds Due September 2069 | Consumers Energy Company |  |
Debt Instrument [Line Items] |  |
Principal balance |  | $ 76
Debt issuance date |  | September 2019
Maturity Date |  | September 2069
Effective interest rate |  | 1.864%
First mortgage bonds due April 2020 | Consumers Energy Company |  |
Debt Instrument [Line Items] |  |
Debt retirement, principal |  | $ 300
Interest Rate |  | 5.65%
Debt retirement date |  | May 2019
Maturity Date |  | April 2020
CMS Energy Corporation |  |
Debt Instrument [Line Items] |  |
Principal balance |  | $ 1,095
Debt retirement, principal |  | 545
CMS Energy Corporation | Term loan facility due December 2019 |  |
Debt Instrument [Line Items] |  |
Principal balance |  | 300
Debt retirement, principal |  | $ 300
Debt issuance date |  | January 2019
Debt retirement date |  | February 2019
Maturity Date |  | December 2019
CMS Energy Corporation | 5.875% Junior Subordinated Notes due 2079 |  |
Debt Instrument [Line Items] |  |
Principal balance |  | $ 630
Interest Rate |  | 5.875%
Debt issuance date |  | February 2019
Maturity Date |  | March 2079
CMS Energy Corporation | Term loan facility due June 2020 |  |
Debt Instrument [Line Items] |  |
Principal balance |  | $ 165
Debt retirement, principal |  | $ 65
Debt issuance date |  | June 2019
Debt retirement date |  | August 2019
Maturity Date |  | June 2020
Effective interest rate |  | 2.552%
CMS Energy Corporation | Term loan facility due April 2019 |  |
Debt Instrument [Line Items] |  |
Debt retirement, principal |  | $ 180
Debt retirement date |  | February 2019
Maturity Date |  | April 2019
London Interbank Offered Rate (LIBOR) | Floating First Rate Mortgage Bonds Due September 2069 | Consumers Energy Company |  |
Debt Instrument [Line Items] |  |
Basis spread on variable rate |  | 0.30%
Term Loan Facility Due June 2020 Tranche One | CMS Energy Corporation | Term loan facility due June 2020 |  |
Debt Instrument [Line Items] |  |
Amount Borrowed |  | $ 5
Term Loan Facility Due June 2020 Tranche One | London Interbank Offered Rate (LIBOR) | CMS Energy Corporation | Term loan facility due June 2020 |  |
Debt Instrument [Line Items] |  |
Basis spread on variable rate |  | 0.50%
Term Loan Facility Due June 2020 Tranche Two | CMS Energy Corporation | Term loan facility due June 2020 |  |
Debt Instrument [Line Items] |  |
Amount Borrowed |  | $ 95
Term Loan Facility Due June 2020 Tranche Two | London Interbank Offered Rate (LIBOR) | CMS Energy Corporation | Term loan facility due June 2020 |  |
Debt Instrument [Line Items] |  |
Basis spread on variable rate |  | 0.50%
Subsequent Event | Term Loan Facility Due June 2020 Tranche One | CMS Energy Corporation | Term loan facility due June 2020 |  |
Debt Instrument [Line Items] |  |
Debt retirement, principal | $ 5 |

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- Definition Date when the debt instrument was partially or fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.). + References No definition available. + Details
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- Definition Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910 + Details
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