Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash Flows from Operating Activities
Net income	$ 384	$ 417	$ 343
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	598	546	576
Deferred income taxes and investment tax credit	227	167	227
Postretirement benefits expense	187	161	213
Bad debt expense	57	74	57
Other non-cash operating activities	16	33	39
Postretirement benefits contributions	(72)	(323)	(463)
Changes in other assets and liabilities
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	(147)	119	(72)
Decrease (increase) in inventories	104	(14)	133
Increase (decrease) in accounts payable	(5)	30	(7)
Increase (decrease) in accrued expenses	(38)	(34)	22
Decrease (increase) in other current and non-current assets	(70)	(7)	(109)
Net cash provided by operating activities	1,241	1,169	959
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(1,227)	(882)	(821)
Cost to retire property	(49)	(54)	(43)
Cash effect of deconsolidation of partnerships			(10)
Increase in EnerBank loans receivable	(63)	(100)	(131)
Other investing activities	(11)	(22)	2
Net cash used in investing activities	(1,350)	(1,058)	(1,003)
Cash Flows from Financing Activities
Proceeds from issuance of long-term debt	1,650	375	1,400
Proceeds from (retirements of) EnerBank notes, net	65	98	149
Issuance of common stock	30	29	10
Retirement of long-term debt	(1,527)	(413)	(878)
Payment of DOE liability		(43)
Payment of common stock dividends	(252)	(211)	(162)
Redemption of preferred stock			(239)
Payment of capital and finance lease obligations and other financing costs	(35)	(34)	(38)
Increase (decrease) in notes payable	110		(40)
Net cash (used in) provided by financing activities	41	(199)	202
Net Increase (Decrease) in Cash and Cash Equivalents, Including Assets Held for Sale	(68)	(88)	158
Decrease (Increase) in Cash and Cash Equivalents Included in Assets Held for Sale		2	(1)
Net Increase (Decrease) in Cash and Cash Equivalents	(68)	(86)	157
Cash and Cash Equivalents, Beginning of Period	161	247	90
Cash and Cash Equivalents, End of Period	93	161	247
Cash transactions
Interest paid (net of amounts capitalized)	377	397	405
Income taxes paid	19	27	14
Non Cash Transactions Abstract
Capital expenditures not paid	110	92	56
Other assets placed under capital lease	9	4	16
Consumers Energy Company [Member]
Cash Flows from Operating Activities
Net income	439	467	434
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	592	542	572
Deferred income taxes and investment tax credit	150	161	246
Postretirement benefits expense	184	158	208
Bad debt expense	53	70	53
Other non-cash operating activities	14	16	24
Postretirement benefits contributions	(68)	(315)	(447)
Changes in other assets and liabilities
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	(145)	112	(59)
Decrease (increase) in inventories	107	(17)	132
Increase (decrease) in accounts payable	7	43	(16)
Increase (decrease) in accrued expenses	51	74	(83)
Decrease (increase) in other current and non-current assets	(31)	12	(154)
Net cash provided by operating activities	1,353	1,323	910
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(1,222)	(876)	(815)
Cost to retire property	(49)	(56)	(43)
Other investing activities	(8)	(19)	(1)
Net cash used in investing activities	(1,279)	(951)	(859)
Cash Flows from Financing Activities
Proceeds from issuance of long-term debt	1,075		600
Retirement of long-term debt	(1,064)	(37)	(482)
Payment of DOE liability		(43)
Payment of common stock dividends	(395)	(376)	(360)
Stockholder contribution	150	125	250
Payment of capital and finance lease obligations and other financing costs	(30)	(27)	(27)
Increase (decrease) in notes payable	110
Net cash (used in) provided by financing activities	(154)	(358)	(19)
Net Increase (Decrease) in Cash and Cash Equivalents	(80)	14	32
Cash and Cash Equivalents, Beginning of Period	85	71	39
Cash and Cash Equivalents, End of Period	5	85	71
Cash transactions
Interest paid (net of amounts capitalized)	224	253	259
Income taxes paid	63	8	149
Non Cash Transactions Abstract
Capital expenditures not paid	110	92	56
Other assets placed under capital lease	$ 9	$ 4	$ 16