Schedule I - Condensed Financial Information of Registrant (Condensed Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash and cash equivalents	$ 93	$ 161	$ 247	$ 90
Notes receivable	41	49
Accounts receivable, including intercompany and related parties	10	10
Deferred income taxes		24
Total current assets	2,422	2,565
Less accumulated depreciation and amortization	5,121	4,901
Investsment in subsidiaries	57	50
Other	293	276
Total other non-current assets	3,158	3,254
Total Assets	17,131	16,452	15,616
Current portion of long-term debt	541	1,057
Accounts and notes payable, including intercompany and related parties	9	9
Accrued interest, including intercompany	95	101
Accrued taxes	279	282
Other liabilities current	152	159
Total current liabilities	1,797	2,338
Long-term debt	6,710	6,040
Unamortized Discount	16	20
Postretirement benefits	1,451	1,289
Other non-current liabilities	311	336
Total non-current liabilities	12,096	11,042
Common stockholders' equity	3,194	3,028
Total Liabilities and Equity	17,131	16,452
CMS Energy [Member]
Cash and cash equivalents	2
Notes receivable	1	1
Accounts receivable, including intercompany and related parties	4	6
Accrued taxes	7	16
Deferred income taxes	3	3
Total current assets	17	26
Plant, property, and equipment, gross	16	16
Less accumulated depreciation and amortization	16	16
Deferred income taxes	392	367
Investsment in subsidiaries	5,312	5,096
Other investments - DB SERP	24	23
Other	26	28
Total other non-current assets	5,754	5,514
Total Assets	5,771	5,540
Current portion of long-term debt	172	398
Accounts and notes payable, including intercompany and related parties	152	163
Accrued interest, including intercompany	30	28
Other liabilities current	5	5
Total current liabilities	359	594
Long-term debt	2,205	1,875
Notes payable - related party		34
Unamortized Discount	(13)	(17)
Postretirement benefits	24	24
Other non-current liabilities	2	2
Total non-current liabilities	2,218	1,918
Common stockholders' equity	3,194	3,028
Total Liabilities and Equity	$ 5,771	$ 5,540