Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Cash Flows from Operating Activities
Net income	$ 317	$ 376
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	440	404
Deferred income taxes and investment tax credit	193	149
Postretirement benefits expense	141	124
Other non-cash operating activities	51	65
Postretirement benefits contributions	(54)	(56)
Changes in other assets and liabilities
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	99	295
Decrease (increase) in inventories	(83)	(106)
Decrease in deferred property taxes	140	133
Increase (decrease) in accounts payable	(16)	10
Increase (decrease) in accrued expenses	(251)	(227)
Decrease (increase) in other current and non-current assets	1	(23)
Increase (decrease) in other current and non-current liabilities	(44)	51
Net cash provided by operating activities	934	1,195
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(861)	(624)
Cost to retire property	(32)	(43)
Increase in EnerBank loans receivable	(32)	(60)
Other investing activities	(13)	(25)
Net cash used in investing activities	(938)	(752)
Cash Flows from Financing Activities
Proceeds from issuance of long-term debt	1,300	375
Proceeds from (retirements of) EnerBank notes, net	25	58
Issuance of common stock	27	26
Retirement of long-term debt	(1,166)	(300)
Payment of DOE liability		(43)
Payment of common stock dividends	(188)	(159)
Payment of capital and finance lease obligations and other financing costs	(27)	(26)
Net cash (used in) provided by financing activities	(29)	(69)
Net Increase (Decrease) in Cash and Cash Equivalents, Including Assets Held for Sale	(33)	374
Decrease (Increase) in Cash and Cash Equivalents Included in Assets Held for Sale		2
Net Increase (Decrease) in Cash and Cash Equivalents	(33)	376
Cash and Cash Equivalents, Beginning of Period	161	247
Cash and Cash Equivalents, End of Period	128	623
Consumers Energy Company [Member]
Cash Flows from Operating Activities
Net income	361	400
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	436	401
Deferred income taxes and investment tax credit	92	85
Postretirement benefits expense	138	117
Other non-cash operating activities	46	52
Postretirement benefits contributions	(51)	(53)
Changes in other assets and liabilities
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	98	283
Decrease (increase) in inventories	(81)	(109)
Decrease in deferred property taxes	140	133
Increase (decrease) in accounts payable	(4)	27
Increase (decrease) in accrued expenses	(143)	(126)
Decrease (increase) in other current and non-current assets	2	(25)
Increase (decrease) in other current and non-current liabilities	(9)	60
Net cash provided by operating activities	1,025	1,245
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(857)	(618)
Cost to retire property	(32)	(43)
Other investing activities	(11)	(22)
Net cash used in investing activities	(900)	(683)
Cash Flows from Financing Activities
Proceeds from issuance of long-term debt	725
Retirement of long-term debt	(703)	(27)
Payment of DOE liability		(43)
Payment of common stock dividends	(302)	(292)
Payment of preferred stock dividends	(2)	(2)
Stockholder contribution	150	125
Payment of capital and finance lease obligations and other financing costs	(21)	(21)
Net cash (used in) provided by financing activities	(153)	(260)
Net Increase (Decrease) in Cash and Cash Equivalents	(28)	302
Cash and Cash Equivalents, Beginning of Period	85	71
Cash and Cash Equivalents, End of Period	$ 57	$ 373