Schedule I - Condensed Financial Information of Registrant (Condensed Statements of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other operating expense									$ (1,236)	$ (1,248)	$ (1,223)
General taxes									284	281	262
Total operating expenses									(5,245)	(5,143)	(5,278)
Operating Loss	$ 379	$ 330	$ 241	$ 388	$ 280	$ 375	$ 275	$ 326	1,338	1,256	1,178
Nonoperating retirement benefits, net									24	41	(15)
Interest income									12	6	12
Other income									6	8	10
Other expense									(76)	(75)	(17)
Total other income (expense)									(14)	5	14
Interest on long-term debt									406	411	386
Intercompany interest expense and other									34	29	14
Total interest charges									438	435	396
Income Before Income Taxes									886	826	796
Income tax expense (benefit)									424	273	271
Net income available to common stockholders	$ (3)	$ 172	$ 92	$ 199	$ 77	$ 186	$ 124	$ 164	460	551	523
CMS Energy [Member]
Other operating expense									(9)	(14)	(8)
Total operating expenses									(9)	(14)	(8)
Operating Loss									(9)	(14)	(8)
Equity earnings of subsidiaries									633	660	625
Nonoperating retirement benefits, net									(1)	(1)	(1)
Interest income									1	1	1
Other income									2
Other expense									(31)	(19)	(9)
Total other income (expense)									604	641	616
Interest on long-term debt									143	150	134
Intercompany interest expense and other									3	1	3
Total interest charges									146	151	137
Income Before Income Taxes									449	476	471
Income tax expense (benefit)									(11)	(75)	(52)
Net income available to common stockholders									$ 460	$ 551	$ 523