Schedule I - Condensed Financial Information of Registrant (Condensed Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current Assets
Notes and accrued interest receivable	$ 233	$ 198
Accounts receivable - intercompany and related parties	14	12
Prepayments and other current assets	101	83
Total current assets	2,468	2,475
Other Non-current Assets
Other	478	799
Total other non-current assets	3,935	3,814
Total Assets	24,529	23,050	$ 21,622
Current Liabilities
Current portion of long-term debt	996	1,103
Accounts and notes payable - intercompany	10	15
Accrued interest, including intercompany	94	103
Other current liabilities	147	195
Total current liabilities	2,624	2,784
Non-current Liabilities
Long-term debt	10,615	9,123
Postretirement benefits	436	766
Other non-current liabilities	294	307
Total non-current liabilities	17,113	15,788
Equity
Common stockholders’ equity	4,755	4,441
Total Liabilities and Equity	24,529	23,050
CMS Energy
Current Assets
Notes and accrued interest receivable	2	5
Accounts receivable - intercompany and related parties	7	7
Federal income tax receivable	44	77
Accrued taxes	26	57
Prepayments and other current assets	1	1
Total current assets	80	147
Other Non-current Assets
Deferred income taxes	180	269
Investments in subsidiaries	7,706	7,202
Other investments – DB SERP	3	25
Other	10	2
Total other non-current assets	7,899	7,498
Total Assets	7,979	7,645
Current Liabilities
Current portion of long-term debt	180	225
Accounts and notes payable - intercompany	113	87
Accrued interest, including intercompany	32	34
Other current liabilities	7	5
Total current liabilities	332	351
Non-current Liabilities
Long-term debt	2,750	2,830
Notes payable - intercompany	116	0
Postretirement benefits	17	21
Other non-current liabilities	9	2
Total non-current liabilities	2,892	2,853
Equity
Total Liabilities and Equity	$ 7,979	$ 7,645