Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Cash Flows from Operating Activities
Net income	$ 352	$ 317
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	463	440
Deferred income taxes and investment tax credit	213	193
Postretirement benefits expense	120	141
Other non-cash operating activities	59	51
Postretirement benefits contributions	(109)	(54)
Proceeds from government grant	69
Cash provided by (used in) changes in assets and liabilities
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	134	99
Decrease (increase) in inventories	(6)	(83)
Decrease in deferred property taxes	140	140
Increase (decrease) in accounts payable	(3)	(16)
Increase (decrease) in accrued expenses	(230)	(251)
Other current and non-current assets and liabilities	(84)	(43)
Net cash provided by operating activities	1,118	934
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(900)	(861)
Cost to retire property	(38)	(32)
Other investing activities	(66)	(45)
Net cash used in investing activities	(1,004)	(938)
Cash Flows from Financing Activities
Proceeds from issuance of long-term debt	1,025	1,300
Proceeds from (retirements of) EnerBank notes, net	48	25
Issuance of common stock	32	27
Retirement of long-term debt	(705)	(1,166)
Payment of common stock dividends	(203)	(188)
Redemption of preferred stock	(7)
Increase (decrease) in notes payable	(110)
Payment of capital lease obligations and other financing costs	(27)	(27)
Net cash provided by (used in) financing activities	53	(29)
Net Increase (Decrease) in Cash and Cash Equivalents	167	(33)
Cash and Cash Equivalents, Beginning of Period	93	161
Cash and Cash Equivalents, End of Period	260	128
Consumers Energy Company [Member]
Cash Flows from Operating Activities
Net income	415	361
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	459	436
Deferred income taxes and investment tax credit	141	92
Postretirement benefits expense	117	138
Other non-cash operating activities	52	46
Postretirement benefits contributions	(106)	(51)
Proceeds from government grant	69
Cash provided by (used in) changes in assets and liabilities
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	135	98
Decrease (increase) in inventories	(5)	(81)
Decrease in deferred property taxes	140	140
Increase (decrease) in accounts payable	7	(4)
Increase (decrease) in accrued expenses	(205)	(143)
Other current and non-current assets and liabilities	(85)	(7)
Net cash provided by operating activities	1,134	1,025
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(895)	(857)
Cost to retire property	(38)	(32)
Other investing activities	(12)	(11)
Net cash used in investing activities	(945)	(900)
Cash Flows from Financing Activities
Proceeds from issuance of long-term debt	750	725
Retirement of long-term debt	(455)	(703)
Payment of common stock dividends	(302)	(304)
Stockholder contribution	150	150
Redemption of preferred stock	(7)
Increase (decrease) in notes payable	(110)
Payment of capital lease obligations and other financing costs	(21)	(21)
Net cash provided by (used in) financing activities	5	(153)
Net Increase (Decrease) in Cash and Cash Equivalents	194	(28)
Cash and Cash Equivalents, Beginning of Period	5	85
Cash and Cash Equivalents, End of Period	$ 199	$ 57