Schedule I - Condensed Financial Information of Registrant (Condensed Statements Of Cash Flows) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income	$ 479	$ 454	$ 384
Deferred income taxes	229	271	226
Accounts and notes receivable	(31)	(120)	(147)
Accounts payable	50	4	(35)
Other current and non-current assets and liabilities	(15)	(88)	(78)
Net cash provided by operating activities	1,447	1,421	1,241
Net cash used in investing activities	(1,910)	(1,532)	(1,350)
Proceeds from issuance of long-term debt	1,428	1,025	1,650
Issuance of common stock	43	36	30
Retirement of long-term debt	(750)	(741)	(1,527)
Increase (decrease) in notes payable	(110)	60	110
Net cash provided by (used in) financing activities	498	190	41
Net Increase (Decrease) in Cash and Cash Equivalents	35	79	(68)
Cash and Cash Equivalents, Beginning of Period	172	93	161
Cash and Cash Equivalents, End of Period	207	172	93
CMS Energy [Member]
Net Income	477	452	382
Equity earnings of subsidiaries	(585)	(566)	(477)
Dividends received from subsidiaries	544	435	401
Deferred income taxes	30	48	(25)
Accounts and notes receivable	(3)	(3)	2
Accounts payable	(2)	2
Accrued taxes	97	48	9
Other current and non-current assets and liabilities	31	18	(14)
Net cash provided by operating activities	589	434	278
Investment in subsidiaries	(495)	(150)	(151)
Return of capital	178
Net cash used in investing activities	(317)	(150)	(151)
Proceeds from issuance of long-term debt	550	275	575
Issuance of common stock	43	36	30
Retirement of long-term debt	(547)	(275)	(463)
Payment of common stock dividends	(293)	(271)	(252)
Debt issuance costs and financing fees	(6)	(4)	(4)
Increase (decrease) in notes payable	(19)	(47)	(11)
Net cash provided by (used in) financing activities	(272)	(286)	(125)
Net Increase (Decrease) in Cash and Cash Equivalents		(2)	2
Cash and Cash Equivalents, Beginning of Period		2
Cash and Cash Equivalents, End of Period			$ 2