Schedule I - Condensed Financial Information of Registrant (Condensed Statements Of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Income	$ 107	$ 148	$ 68	$ 202	$ 97	$ 94	$ 84	$ 204	$ 525	$ 479	$ 454
Deferred income taxes									228	229	271
Accounts and notes receivable									120	(31)	(120)
Accounts payable									(26)	50	4
Other current and non-current assets and liabilities									(19)	(15)	(88)
Net cash provided by operating activities									1,640	1,447	1,421
Net cash used in investing activities									(2,044)	(1,910)	(1,532)
Proceeds from issuance of debt									599	1,428	1,025
Issuance of common stock									43	43	36
Retirement of long-term debt									(224)	(750)	(741)
Increase (decrease) in notes payable									189	(110)	60
Net cash provided by financing activities									463	498	190
Net Increase (Decrease) in Cash and Cash Equivalents									59	35	79
Cash and Cash Equivalents, Beginning of Period				$ 207				$ 172	207	172	93
Cash and Cash Equivalents, End of Period	$ 266				$ 207				266	207	172
CMS Energy [Member]
Net Income									523	477	452
Equity earnings of subsidiaries									(625)	(585)	(566)
Dividends received from subsidiaries									499	544	435
Deferred income taxes									(24)	30	48
Accounts and notes receivable									(86)	(3)	(3)
Accounts payable									16	(2)	2
Accrued taxes									(115)	97	48
Other current and non-current assets and liabilities									21	31	18
Net cash provided by operating activities									209	589	434
Investment in subsidiaries									(150)	(495)	(150)
Return of capital										178
Net cash used in investing activities									(150)	(317)	(150)
Proceeds from issuance of debt									349	550	275
Issuance of common stock									43	43	36
Retirement of long-term debt									(100)	(547)	(275)
Payment of dividends on common stock									(320)	(293)	(271)
Debt issuance costs and financing fees									(3)	(6)	(4)
Increase (decrease) in notes payable									(28)	(19)	(47)
Net cash provided by financing activities									$ (59)	$ (272)	(286)
Net Increase (Decrease) in Cash and Cash Equivalents											(2)
Cash and Cash Equivalents, Beginning of Period											$ 2
Cash and Cash Equivalents, End of Period