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Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Income Taxes [Line Items]      
Income from continuing operataions before income taxes $ 796 $ 729 $ 756
Income tax expense at statutory rate 279 255 265
State and local income taxes, net of federal effect 39 36 37
Accelerated flow-through of regulatory tax benefits (39) (39)  
Other, net (8) (2)  
Income Tax Expense $ 271 $ 250 $ 302
Effective income tax rate 34.00% 34.30% 39.90%
Consumers Energy Company [Member]      
Income Taxes [Line Items]      
Income from continuing operataions before income taxes $ 896 $ 873 $ 880
Income tax expense at statutory rate 314 306 308
State and local income taxes, net of federal effect 42 42 43
Accelerated flow-through of regulatory tax benefits (39) (39)  
Other, net (15) (3) (5)
Income Tax Expense $ 302 $ 306 $ 346
Effective income tax rate 33.70% 35.10% 39.30%