Schedule I - Condensed Financial Information of Registrant (Condensed Statements Of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Income	$ 78	$ 186	$ 125	$ 164	$ 107	$ 148	$ 68	$ 202	$ 553	$ 525	$ 479
Deferred income taxes									247	228	229
Other non-cash operating activities and reconciling adjustments									52	100	58
Accounts and notes receivable									(155)	120	(31)
Accounts payable									59	(26)	50
Other current and non-current assets and liabilities									(43)	(19)	1
Net cash provided by operating activities									1,629	1,640	1,481
Net cash used in investing activities									(1,915)	(2,064)	(1,898)
Proceeds from issuance of debt									1,049	599	1,428
Issuance of common stock									72	43	43
Retirement of long-term debt									(728)	(224)	(750)
Debt prepayment costs									(18)		(36)
Increase (decrease) in notes payable									149	189	(110)
Net cash provided by (used in) financing activities									255	463	462
Net Increase in Cash and Cash Equivalents, Including Restricted Amounts									(31)	39	45
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period				288				249	288	249	204
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	257				288				257	288	249
CMS Energy [Member]
Net Income									551	523	477
Equity earnings of subsidiaries									(660)	(625)	(585)
Dividends received from subsidiaries									499	499	544
Deferred income taxes									(26)	(24)	30
Other non-cash operating activities and reconciling adjustments									18		20
Accounts and notes receivable									85	(86)	(3)
Accounts payable									(9)	16	(2)
Accrued taxes									(74)	(115)	97
Other current and non-current assets and liabilities									38	21	31
Net cash provided by operating activities									422	209	609
Investment in subsidiaries									(275)	(150)	(495)
Return of capital											178
Net cash used in investing activities									(275)	(150)	(317)
Proceeds from issuance of debt									603	349	550
Issuance of common stock									72	43	43
Retirement of long-term debt									(530)	(100)	(547)
Debt prepayment costs									(18)		(20)
Payment of dividends on common stock									(345)	(320)	(293)
Debt issuance costs and financing fees									(5)	(3)	(6)
Increase (decrease) in notes payable									76	(28)	(19)
Net cash provided by (used in) financing activities									(147)	(59)	(292)
Net Increase in Cash and Cash Equivalents, Including Restricted Amounts
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period
Cash and Cash Equivalents, Including Restricted Amounts, End of Period