Schedule I - Condensed Financial Information of Registrant (Condensed Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current Assets
Accounts receivable – intercompany and related parties	$ 19	$ 17
Prepayments and other current assets	112	86
Total current assets	2,404	2,331
Other Non‑current Assets
Other	869	739
Total other non‑current assets	6,223	5,580
Total Assets	29,666	26,837	$ 24,529
Current Liabilities
Accounts and notes payable – intercompany	7	13
Accrued interest, including intercompany	106	104
Accrued taxes	457	437
Other current liabilities	156	186
Total current liabilities	3,074	2,704
Non‑current Liabilities
Long-term debt	13,634	11,951
Postretirement benefits	152	674
Other non‑current liabilities	398	383
Total non‑current liabilities	20,515	19,078
Equity
Common stockholders’ equity	5,496	5,018
Total Liabilities and Equity	29,666	26,837
CMS Energy
Current Assets
DB SERP note receivable – related party	358	2
Accounts receivable – intercompany and related parties	3	9
Federal income tax receivable	0	18
Accrued taxes	48	0
Prepayments and other current assets	1	1
Total current assets	410	30
Other Non‑current Assets
Deferred income taxes	91	126
Investments in subsidiaries	9,372	8,526
Other investments	5	4
Other	5	16
Total other non‑current assets	9,473	8,672
Total Assets	9,883	8,702
Current Liabilities
Current portion of long-term debt	200	0
Accounts and notes payable – intercompany	69	123
Accrued interest, including intercompany	33	34
Accrued taxes	0	5
Other current liabilities	9	38
Total current liabilities	311	200
Non‑current Liabilities
Long-term debt	3,926	3,334
Notes payable – intercompany	116	112
Postretirement benefits	21	21
Other non‑current liabilities	13	17
Total non‑current liabilities	4,076	3,484
Equity
Common stockholders’ equity	5,496	5,018
Total Liabilities and Equity	$ 9,883	$ 8,702