Schedule I - Condensed Financial Information of Registrant (Condensed Statements of Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other operating expense									$ (1,232)	$ (1,236)	$ (1,224)
General taxes									252	234	229
Total operating expenses									(6,027)	(5,424)	(5,250)
Operating Loss	273	236	235	408	264	317	232	329	1,152	1,142	1,003
Interest income									5	3	5
Total other income (expense)									(16)	12	8
Interest on long-term debt									393	385	372
Intercompany interest expense and other									17	16	21
Total interest charges									407	398	389
Income Before Income Taxes									729	756	622
Income Tax Expense									250	302	245
Income From Continuing Operations									479	454	377
Income From Discontinued Operations, Net of Tax											7
Net income attributable to CMS Energy	96	94	83	204	102	126	80	144	477	452	382
CMS Energy [Member]
Other operating expense									(6)	(6)	(8)
Total operating expenses									(6)	(6)	(8)
Operating Loss									(6)	(6)	(8)
Equity earnings of subsidiaries									585	566	477
Interest income									1	1	1
Other expense									(20)	(8)	(5)
Total other income (expense)									566	559	473
Interest on long-term debt									150	148	140
Intercompany interest expense and other									2	3	5
Total interest charges									152	151	145
Income Before Income Taxes									408	402	320
Income Tax Expense									(69)	(50)	(62)
Income From Continuing Operations									477	452	382
Net income attributable to CMS Energy									$ 477	$ 452	$ 382