Schedule I - Condensed Financial Information of Registrant (Condensed Statements Of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows from Operating Activities
Net cash provided by operating activities	$ 1,790	$ 1,703	$ 1,705
Cash Flows from Investing Activities
Proceeds from DB SERP investments	0	146	0
Net cash used in investing activities	(2,816)	(2,606)	(1,868)
Cash Flows from Financing Activities
Proceeds from issuance of debt	2,151	2,767	1,633
Issuance of common stock	12	41	83
Retirement of long-term debt	(1,285)	(1,870)	(980)
Debt prepayment costs	(8)	(36)	(22)
Payment of dividends on common stock	(436)	(407)	(377)
Net cash provided by financing activities	1,008	874	110
Net Decrease in Cash and Cash Equivalents, Including Restricted Amounts	(18)	(29)	(53)
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	175	204	257
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	157	175	204
CMS Energy
Cash Flows from Operating Activities
Net cash provided by operating activities	697	702	433
Cash Flows from Investing Activities
Investment in subsidiaries	(683)	(363)	(447)
Proceeds from DB SERP investments	0	22	0
Net cash used in investing activities	(683)	(341)	(447)
Cash Flows from Financing Activities
Proceeds from issuance of debt	1,158	560	799
Issuance of common stock	12	41	83
Retirement of long-term debt	(738)	(675)	(425)
Debt prepayment costs	0	(16)	(18)
Payment of dividends on common stock	(434)	(405)	(375)
Debt issuance costs and financing fees	(18)	(8)	(3)
Change in notes payable – intercompany	6	142	(47)
Net cash provided by financing activities	(14)	(361)	14
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