Schedule I - Condensed Financial Information of Registrant (Condensed Balance Sheets) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Notes and accrued interest receivable		$ 128	$ 98
Accounts receivable, including intercompany and related parties		11	11
Total current assets		2,320	2,597
Less accumulated depreciation and amortization		5,747	5,415
Total plant, property, and equipment	[1]	14,705	13,412
Other		384	352
Total other non-current assets		3,315	3,176
Total Assets		20,340	19,185	$ 17,290
Current portion of long-term debt		706	540
Accounts and notes payable, including intercompany and related parties		9	10
Accrued interest, including intercompany		106	108
Accrued taxes		349	316
Other liabilities current		142	163
Total current liabilities		2,302	1,948
Long-term debt		8,441	8,016
Net unamortized discounts		(12)	(12)
Postretirement benefits		591	872
Other non-current liabilities		313	299
Total non-current liabilities		14,063	13,530
Common stockholders' equity		3,938	3,670
Total Liabilities and Equity		20,340	19,185
CMS Energy [Member]
Notes and accrued interest receivable		88	2
Accounts receivable, including intercompany and related parties		9	9
Total current assets		97	11
Plant, property, and equipment, gross		16	16
Less accumulated depreciation and amortization		$ 16	$ 16
Total plant, property, and equipment
Deferred income taxes		$ 340	$ 317
Invetment in subsidiaries		6,240	5,961
Other investments - DB SERP		26	22
Other		23	23
Total other non-current assets		6,629	6,323
Total Assets		6,726	6,334
Accounts and notes payable, including intercompany and related parties		74	86
Accrued interest, including intercompany		38	37
Accrued taxes		23	138
Other liabilities current		5	4
Total current liabilities		140	265
Long-term debt		2,630	2,380
Net unamortized discounts		(7)	(7)
Postretirement benefits		22	24
Other non-current liabilities		3	2
Total non-current liabilities		2,648	2,399
Common stockholders' equity		3,938	3,670
Total Liabilities and Equity		$ 6,726	$ 6,334

[1] For the year ended December 31, 2015, utility plant additions were $1.4 billion and utility plant retirements were $187 million. For the year ended December 31, 2014, utility plant additions were $1.6 billion and utility plant retirements were $126 million.