Schedule I - Condensed Financial Information of Registrant (Condensed Statements Of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows from Operating Activities
Net cash provided by operating activities	$ 1,703	$ 1,705	$ 1,629
Cash Flows from Investing Activities
Proceeds from DB SERP investments	146	0	0
Net cash used in investing activities	(2,606)	(1,868)	(1,915)
Cash Flows from Financing Activities
Proceeds from issuance of debt	2,767	1,633	1,049
Issuance of common stock	41	83	72
Retirement of long-term debt	(1,870)	(980)	(728)
Debt prepayment costs	(36)	(22)	(18)
Payment of dividends on common stock	(407)	(377)	(347)
Net cash provided by financing activities	874	110	255
Net Decrease in Cash and Cash Equivalents, Including Restricted Amounts	(29)	(53)	(31)
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	204	257	288
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	175	204	257
CMS Energy
Cash Flows from Operating Activities
Net cash provided by operating activities	702	433	422
Cash Flows from Investing Activities
Investment in subsidiaries	(363)	(447)	(275)
Proceeds from DB SERP investments	22	0	0
Net cash used in investing activities	(341)	(447)	(275)
Cash Flows from Financing Activities
Proceeds from issuance of debt	560	799	603
Issuance of common stock	41	83	72
Retirement of long-term debt	(675)	(425)	(530)
Debt prepayment costs	(16)	(18)	(18)
Payment of dividends on common stock	(405)	(375)	(345)
Debt issuance costs and financing fees	(8)	(3)	(5)
Change in notes payable - intercompany	142	(47)	76
Net cash provided by financing activities	(361)	14	(147)
Net Decrease in Cash and Cash Equivalents, Including Restricted Amounts	0	0	0
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	0	0	0
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	$ 0	$ 0	$ 0