Schedule I - Condensed Financial Information of Registrant (Condensed Statements of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Expenses
Other operating expense									$ (1,448)	$ (1,417)	$ (1,236)
Total operating expenses									(5,606)	(5,711)	(5,245)
Operating Loss	$ 311	$ 351	$ 218	$ 359	$ 250	$ 294	$ 255	$ 363	1,239	1,162	1,338
Other Income and Expenses [Abstract]
Nonoperating retirement benefits, net									91	90	24
Interest income									7	11	12
Other income									4	2	6
Other expense									(13)	(48)	(76)
Total other income (expense)									109	70	(14)
Interest Charges
Interest on long-term debt									439	412	406
Interest on long-term debt									75	49	34
Total interest charges									519	458	438
Income Before Income Taxes									829	774	886
Income tax expense (benefit)									147	115	424
Net income (loss) available to common stockholders	$ 167	$ 207	$ 93	$ 213	$ 108	$ 169	$ 139	$ 241	680	657	460
CMS Energy
Operating Expenses
Other operating expense									(38)	(7)	(9)
Total operating expenses									(38)	(7)	(9)
Operating Loss									(38)	(7)	(9)
Other Income and Expenses [Abstract]
Equity earnings of subsidiaries									826	780	633
Nonoperating retirement benefits, net									(1)	(1)	(1)
Interest income									1	2	1
Other income									1	0	2
Other expense									0	17	31
Total other income (expense)									827	764	604
Interest Charges
Interest on long-term debt									156	135	143
Interest on long-term debt									10	7	3
Total interest charges									166	142	146
Income Before Income Taxes									623	615	449
Income tax expense (benefit)									(57)	(42)	(11)
Net income (loss) available to common stockholders									$ 680	$ 657	$ 460