Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Liabilities
Current accounts receivable	$ 12,000,000	$ 13,000,000
EnerBank notes receivable, net of allowance for loan losses	275,000,000	242,000,000
Current portion of long term debt	1,486,000,000	1,111,000,000
Current portion of long-term payables	6,000,000	1,000,000
Carrying Amount
Assets
Long-term receivables	17,000,000	20,000,000
Notes receivable	2,887,000,000	2,500,000,000
Debt Securities, Held-to-maturity, Fair Value	28,000,000	26,000,000
Liabilities
Long-term debt	15,120,000,000	13,062,000,000
Long-term payables	33,000,000	30,000,000
Fair Value
Assets
Long-term receivables	17,000,000	20,000,000
Notes receivable	3,248,000,000	2,652,000,000
Debt Securities, Held-to-maturity, Fair Value	29,000,000	26,000,000
Liabilities
Long-term debt	17,512,000,000	14,185,000,000
Long-term payables	35,000,000	32,000,000
Consumers Energy Company
Liabilities
Current portion of long term debt	364,000,000	202,000,000
DB SERP note receivable – related party	7,000,000	7,000,000
Consumers Energy Company | Carrying Amount
Assets
Long-term receivables	17,000,000	20,000,000
Notes receivable related party	107,000,000	103,000,000
Liabilities
Long-term debt	8,106,000,000	7,250,000,000
Consumers Energy Company | Fair Value
Assets
Long-term receivables	17,000,000	20,000,000
Notes receivable related party	107,000,000	103,000,000
Liabilities
Long-term debt	9,801,000,000	8,010,000,000
Fair Value, Inputs, Level 1 | Fair Value
Assets
Long-term receivables	0	0
Notes receivable	0	0
Debt Securities, Held-to-maturity, Fair Value	0	0
Liabilities
Long-term debt	1,249,000,000	1,197,000,000
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
Debt Securities, Held-to-maturity, Fair Value	29,000,000	26,000,000
Liabilities
Long-term debt	14,178,000,000	11,048,000,000
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	7,716,000,000	6,070,000,000
Level 3 | Fair Value
Assets
Long-term receivables	17,000,000	20,000,000
Notes receivable	3,248,000,000	2,652,000,000
Debt Securities, Held-to-maturity, Fair Value	0	0
Liabilities
Long-term debt	2,085,000,000	1,940,000,000
Long-term payables	35,000,000	32,000,000
Level 3 | Consumers Energy Company | Fair Value
Assets
Long-term receivables	17,000,000	20,000,000
Notes receivable related party	107,000,000	103,000,000
Liabilities
Long-term debt	2,085,000,000	1,940,000,000
EnerBank
Liabilities
EnerBank notes receivable, net of allowance for loan losses	275,000,000	242,000,000
Unrealized gain on mortgage backed security	$ 1,000,000	$ 0