Consolidated Statements Of Cash Flows (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash Flows from Operating Activities
Net income	$ 144	$ 67
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	181	172
Deferred income taxes and investment tax credit	87	42
Postretirement benefits expense	47	47
Other non-cash operating activities	19	19
Postretirement benefits contributions	(68)	(19)
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	(103)	99
Decrease (increase) in inventories	447	312
Increase (decrease) in accounts payable	(44)	(89)
Increase (decrease) in accrued expenses	(101)	(109)
Decrease (increase) in other current and non-current assets	47	94
Net cash provided by operating activities	725	635
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(274)	(294)
Cost to retire property	(9)	(7)
Other investing activities	(10)	(12)
Net cash used in investing activities	(293)	(313)
Cash Flows from Financing Activities
Proceeds from issuance of long-term debt	250	390
Proceeds from (retirements of) EnerBank notes, net	(16)	15
Issuance of common stock	24	1
Retirement of long-term debt	(10)	(459)
Payment of common stock dividends	(67)	(62)
Increase (decrease) in notes payable	(110)
Payment of capital and finance lease obligations and other financing costs	(10)	(10)
Net cash provided by (used in) financing activities	61	(125)
Net Increase in Cash and Cash Equivalents	493	197
Cash and Cash Equivalents, Beginning of Period	93	161
Cash and Cash Equivalents, End of Period	586	358
Consumers Energy Company [Member]
Cash Flows from Operating Activities
Net income	162	76
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	180	171
Deferred income taxes and investment tax credit	44	20
Postretirement benefits expense	47	46
Other non-cash operating activities	18	19
Postretirement benefits contributions	(67)	(18)
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	(102)	100
Decrease (increase) in inventories	442	302
Increase (decrease) in accounts payable	(44)	(74)
Increase (decrease) in accrued expenses	(80)	(69)
Decrease (increase) in other current and non-current assets	44	108
Net cash provided by operating activities	713	681
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(273)	(294)
Cost to retire property	(9)	(7)
Other investing activities	(13)	(11)
Net cash used in investing activities	(295)	(312)
Cash Flows from Financing Activities
Retirement of long-term debt	(10)	(310)
Payment of common stock dividends	(93)	(115)
Stockholder contribution	150	150
Increase (decrease) in notes payable	(110)
Payment of capital and finance lease obligations and other financing costs	(5)	(6)
Net cash provided by (used in) financing activities	(68)	(281)
Net Increase in Cash and Cash Equivalents	350	88
Cash and Cash Equivalents, Beginning of Period	5	85
Cash and Cash Equivalents, End of Period	$ 355	$ 173