Schedule I - Condensed Financial Information of Registrant (Condensed Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Cash and cash equivalents	$ 207		$ 172		$ 93	$ 161
Notes and accrued interest receivable	98		63
Accounts receivable, including intercompany and related parties	11		10
Deferred income taxes			126
Total current assets	2,597		2,526
Less accumulated depreciation and amortization	5,415		5,087
Total plant, property, and equipment	13,412	[1]	12,246	[1]
Other	352		409
Total other non-current assets	3,176		2,644
Total Assets	19,185		17,416		17,131
Current portion of long-term debt	540		562
Accounts and notes payable, including intercompany and related parties	10		10
Accrued interest, including intercompany	108		96
Accrued taxes	316		297
Other liabilities current	163		146
Total current liabilities	2,014		1,945
Long-term debt	8,016		7,101
Net unamortized discount	(12)		(12)
Postretirement benefits	872		239
Other non-current liabilities	299		306
Total non-current liabilities	13,464		11,980
Common stockholders' equity	3,670		3,454
Total Liabilities and Equity	19,185		17,416
CMS Energy [Member]
Cash and cash equivalents					2
Notes and accrued interest receivable	2		1
Accounts receivable, including intercompany and related parties	9		7
Deferred income taxes	3		2
Total current assets	14		10
Plant, property, and equipment, gross	16		16
Less accumulated depreciation and amortization	16		16
Total plant, property, and equipment
Deferred income taxes	314		345
Invetment in subsidiaries	5,961		5,626
Other investments - DB SERP	22		23
Other	23		23
Total other non-current assets	6,320		6,017
Total Assets	6,334		6,027
Current portion of long-term debt			172
Accounts and notes payable, including intercompany and related parties	86		107
Accrued interest, including intercompany	37		32
Accrued taxes	138		41
Other liabilities current	4		4
Total current liabilities	265		356
Long-term debt	2,380		2,205
Net unamortized discount	(7)		(9)
Postretirement benefits	24		19
Other non-current liabilities	2		2
Total non-current liabilities	2,399		2,217
Common stockholders' equity	3,670		3,454
Total Liabilities and Equity	$ 6,334		$ 6,027

[1] For the year ended December 31, 2014, utility plant additions were $1.6 billion and utility plant retirements were $126 million. For the year ended December 31, 2013, utility plant additions were $1.3 billion and utility plant retirements were $156 million.