Schedule I - Condensed Financial Information of Registrant (Condensed Balance Sheets) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Balance Sheet Statements, Captions [Line Items]
Notes and accrued interest receivable		$ 198	$ 180
Accounts receivable, including intercompany and related parties		12	12
Prepayments and other current assets		83	81
Total current assets		2,475	2,280
Less accumulated depreciation and amortization		6,510	6,056
Total plant, property, and equipment	[1]	16,761	15,715
Other		799	353
Total other non-current assets		3,814	3,627
Total Assets		23,050	21,622	$ 20,299
Current portion of long-term debt		1,103	886
Accounts and notes payable, including intercompany and related parties		15	12
Accrued interest, including intercompany		103	98
Accrued taxes		360	348
Other liabilities current		195	199
Total current liabilities		2,784	2,655
Long-term debt		9,123	8,640
Net unamortized discounts		(14)	(15)
Postretirement benefits		766	789
Other non-current liabilities		307	290
Total non-current liabilities		15,788	14,677
Common stockholders' equity		4,441	4,253
Total Liabilities and Equity		23,050	21,622
CMS Energy [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Notes and accrued interest receivable		5	2
Accounts receivable, including intercompany and related parties		7	7
Federal income tax receivable		77
Accrued taxes		57	51
Prepayments and other current assets		1	1
Total current assets		147	61
Noncurrent notes receivable			3
Deferred income taxes		269	366
Invetment in subsidiaries		7,202	6,674
Other investments - DB SERP		25	26
Other		2	4
Total other non-current assets		7,498	7,073
Total Assets		7,645	7,134
Current portion of long-term debt		225
Accounts and notes payable, including intercompany and related parties		87	141
Accrued interest, including intercompany		34	28
Other liabilities current		5	10
Total current liabilities		351	179
Long-term debt		2,830	2,678
Postretirement benefits		21	21
Other non-current liabilities		2	3
Total non-current liabilities		2,853	2,702
Common stockholders' equity		4,441	4,253
Total Liabilities and Equity		$ 7,645	$ 7,134

[1] For the year ended December 31, 2017, Consumers' plant additions were $1.7 billion and plant retirements were $214 million. For the year ended December 31, 2016, Consumers' plant additions were $2.3 billion and plant retirements were $285 million.