Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Liabilities
Current accounts receivable	$ 11,000,000	$ 12,000,000
EnerBank notes receivable, net of allowance for loan losses	284,000,000	275,000,000
Current portion of long term debt	1,500,000,000	1,500,000,000
Current portion of long-term payables	6,000,000	6,000,000
Carrying Amount
Assets
Long-term receivables	16,000,000	17,000,000
Notes receivable	2,710,000,000	2,887,000,000
Securities held to maturity	34,000,000	28,000,000
Liabilities
Long-term debt	15,046,000,000	15,120,000,000
Long-term payables	33,000,000	33,000,000
Fair Value
Assets
Long-term receivables	16,000,000	17,000,000
Notes receivable	3,006,000,000	3,248,000,000
Securities held to maturity	34,000,000	29,000,000
Liabilities
Long-term debt	16,233,000,000	17,512,000,000
Long-term payables	35,000,000	35,000,000
Consumers Energy Company
Liabilities
Current portion of long term debt	364,000,000	364,000,000
DB SERP note receivable – related party	7,000,000	7,000,000
Consumers Energy Company | Carrying Amount
Assets
Long-term receivables	16,000,000	17,000,000
Notes receivable related party	106,000,000	107,000,000
Liabilities
Long-term debt	8,107,000,000	8,106,000,000
Consumers Energy Company | Fair Value
Assets
Long-term receivables	16,000,000	17,000,000
Notes receivable related party	106,000,000	107,000,000
Liabilities
Long-term debt	8,815,000,000	9,801,000,000
Fair Value, Inputs, Level 1 | Fair Value
Assets
Long-term receivables	0	0
Notes receivable	0	0
Securities held to maturity	0	0
Liabilities
Long-term debt	1,206,000,000	1,249,000,000
Long-term payables	0	0
Fair Value, Inputs, Level 1 | Consumers Energy Company | Fair Value
Assets
Long-term receivables	0	0
Notes receivable related party	0	0
Liabilities
Long-term debt	0	0
Level 2 | Fair Value
Assets
Long-term receivables	0	0
Notes receivable	0	0
Securities held to maturity	34,000,000	29,000,000
Liabilities
Long-term debt	13,108,000,000	14,178,000,000
Long-term payables	0	0
Level 2 | Consumers Energy Company | Fair Value
Assets
Long-term receivables	0	0
Notes receivable related party	0	0
Liabilities
Long-term debt	6,896,000,000	7,716,000,000
Level 3 | Fair Value
Assets
Long-term receivables	16,000,000	17,000,000
Notes receivable	3,006,000,000	3,248,000,000
Securities held to maturity	0	0
Liabilities
Long-term debt	1,919,000,000	2,085,000,000
Long-term payables	35,000,000	35,000,000
Level 3 | Consumers Energy Company | Fair Value
Assets
Long-term receivables	16,000,000	17,000,000
Notes receivable related party	106,000,000	107,000,000
Liabilities
Long-term debt	1,919,000,000	2,085,000,000
EnerBank
Liabilities
EnerBank notes receivable, net of allowance for loan losses	284,000,000	275,000,000
Unrealized gain on mortgage backed security	$ 0	$ 1,000,000