Reportable Segments (Reconciliation of Revenue from Segments to Consolidated) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011	Dec. 31, 2011
Operating Revenue	$ 1,333		$ 1,364	$ 3,076		$ 3,419
Total Net Income Available to Common Stockholders	100		100	167		235
Total Plant, Property, and Equipment, Gross	14,959			14,959			14,751
Total Assets	16,293			16,293			16,452
Consumers Energy Company [Member]
Operating Revenue	1,282		1,303	2,957		3,291
Total Net Income Available to Common Stockholders	121		91	197		244
Total Plant, Property, and Equipment, Gross	14,825			14,825			14,621
Total Assets	15,554			15,554			15,662
Electric Utility [Member]
Operating Revenue	998		949	1,834		1,846
Total Net Income Available to Common Stockholders	111		85	132		150
Total Plant, Property, and Equipment, Gross	10,549			10,549			10,400
Total Assets	10,157	[1]		10,157	[1]		9,938	[1]
Electric Utility [Member] | Consumers Energy Company [Member]
Operating Revenue	998		949	1,834		1,846
Total Net Income Available to Common Stockholders	111		85	132		150
Total Plant, Property, and Equipment, Gross	10,549			10,549			10,400
Total Assets	10,157	[1]		10,157	[1]		9,938	[1]
Gas Utility [Member]
Operating Revenue	284		354	1,123		1,445
Total Net Income Available to Common Stockholders	9		5	64		93
Total Plant, Property, and Equipment, Gross	4,261			4,261			4,206
Total Assets	4,770	[1]		4,770	[1]		4,956	[1]
Gas Utility [Member] | Consumers Energy Company [Member]
Operating Revenue	284		354	1,123		1,445
Total Net Income Available to Common Stockholders	9		5	64		93
Total Plant, Property, and Equipment, Gross	4,261			4,261			4,206
Total Assets	4,770	[1]		4,770	[1]		4,956	[1]
Enterprises [Member]
Operating Revenue	38		50	92		105
Total Net Income Available to Common Stockholders	(1)		29	4		32
Total Plant, Property, and Equipment, Gross	112			112			109
Total Assets	177			177			242
Other [Member]
Operating Revenue	13		11	27		23
Total Net Income Available to Common Stockholders	(19)		(19)	(33)		(40)
Total Plant, Property, and Equipment, Gross	37			37			36
Total Assets	1,189			1,189			1,316
Other [Member] | Consumers Energy Company [Member]
Total Net Income Available to Common Stockholders	1		1	1		1
Total Plant, Property, and Equipment, Gross	15			15			15
Total Assets	$ 627			$ 627			$ 768

[1] 1 Amounts include a portion of Consumers' other common assets attributable to both the electric and gas utility businesses.