Financial Instruments (Schedule Of Carrying Amounts And Fair Values Of Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Liabilities
Current accounts receivable	$ 9	$ 12
Current portion of long term debt	572	571
Current portion of long-term payables	22	6
Carrying Amount
Assets
Long-term receivables	14	17
Liabilities
Long-term debt	12,599	12,315
Long-term payables	31	33
Fair Value
Assets
Long-term receivables	14	17
Liabilities
Long-term debt	13,886	14,601
Long-term payables	32	35
Consumers Energy Company
Liabilities
Current accounts receivable	9	12
Current portion of long term debt	364	364
DB SERP note receivable – related party	7	7
Consumers Energy Company | Carrying Amount
Assets
Long-term receivables	14	17
Notes receivable related party	104	107
Liabilities
Long-term debt	8,392	8,106
Consumers Energy Company | Fair Value
Assets
Long-term receivables	14	17
Notes receivable related party	104	107
Liabilities
Long-term debt	9,411	9,801
Level 1 | Fair Value
Assets
Long-term receivables	0	0
Liabilities
Long-term debt	1,195	1,249
Long-term payables	0	0
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
Liabilities
Long-term debt	10,727	11,267
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	7,447	7,716
Level 3 | Fair Value
Assets
Long-term receivables	14	17
Liabilities
Long-term debt	1,964	2,085
Long-term payables	32	35
Level 3 | Consumers Energy Company | Fair Value
Assets
Long-term receivables	14	17
Notes receivable related party	104	107
Liabilities
Long-term debt	$ 1,964	$ 2,085