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Financings And Capitalization (Major Long-Term Debt Transactions) (Details) | 12 Months Ended
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Dec. 31, 2016 USD ($)
Debt Instrument [Line Items] |  |
Principal Balance | $ 1,025,000,000 |
Debt retirement, principal | 673,000,000 |
CMS Energy [Member] |  |
Debt Instrument [Line Items] |  |
Principal Balance | 575,000,000 |
Debt retirement, principal | 500,000,000 |
Consumers Energy Company [Member] |  |
Debt Instrument [Line Items] |  |
Principal Balance | 450,000,000 |
Debt retirement, principal | $ 173,000,000 |
Senior Notes 3.000% Due May 2026 [Member] |  |
Debt Instrument [Line Items] |  |
Interest rate | 3.00% |
Senior Notes 3.000% Due May 2026 [Member] | CMS Energy [Member] |  |
Debt Instrument [Line Items] |  |
Principal Balance | $ 300,000,000 |
Interest rate | 3.00% |
Debt issuance date | May 2016 |
Maturity date | May 2026 |
Senior Notes 2.950% Due 2027 [Member] |  |
Debt Instrument [Line Items] |  |
Interest rate | 2.95% |
Senior Notes 2.950% Due 2027 [Member] | CMS Energy [Member] |  |
Debt Instrument [Line Items] |  |
Principal Balance | $ 275,000,000 |
Interest rate | 2.95% |
Debt issuance date | November 2016 |
Maturity date | February 2027 |
Senior Notes 6.550% Due 2017 [Member] | CMS Energy [Member] |  |
Debt Instrument [Line Items] |  |
Debt retirement, principal | $ 250,000,000 |
Interest rate | 6.55% |
Debt retirement date | December 2016 |
Maturity date | July 2017 |
Senior Notes 5.050% Due 2022 [Member] | CMS Energy [Member] |  |
Debt Instrument [Line Items] |  |
Debt retirement, principal | $ 250,000,000 |
Interest rate | 5.05% |
Debt retirement date | December 2016 |
Maturity date | February 2018 |
FMB's 3.250% Due 2046 [Member] | Consumers Energy Company [Member] |  |
Debt Instrument [Line Items] |  |
Principal Balance | $ 450,000,000 |
Interest rate | 3.25% | [1]
Debt issuance date | August 2016 |
Maturity date | August 2046 |
FMB's 5.500% Due 2016 [Member] | Consumers Energy Company [Member] |  |
Debt Instrument [Line Items] |  |
Debt retirement, principal | $ 173,000,000 |
Interest rate | 5.50% |
Debt retirement date | August 2016 |
Maturity date | August 2016 |
[1] | The weighted-average interest rate for Consumers' first mortgage bonds was 4.57 percent at December 31, 2016 and 4.73 percent at December 31, 2015.

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