Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Cash Flows from Operating Activities
Net income	$ 168	$ 236
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	302	284
Deferred income taxes and investment tax credit	102	74
Postretirement benefits expense	94	83
Other non-cash operating activities	35	39
Postretirement benefits contributions	(37)	(39)
Changes in other assets and liabilities:
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	146	215
Decrease (increase) in accrued power supply revenue		15
Decrease (increase) in inventories	135	204
Increase (decrease) in accounts payable	10	34
Increase (decrease) in accrued expenses	(82)	(36)
Decrease (increase) in other current and non-current assets	100	71
Increase (decrease) in other current and non-current liabilities	(30)	36
Net cash provided by operating activities	943	1,216
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(575)	(399)
Cost to retire property	(20)	(28)
Other investing activities	(15)	(44)
Net cash used in investing activities	(610)	(471)
Cash Flows from Financing Activities
Proceeds from issuance of long-term debt	790	375
Proceeds from EnerBank notes, net	(4)	21
Issuance of common stock	23	22
Retirement of long-term debt	(972)	(292)
Payment of common stock dividends	(125)	(106)
Payment of capital and finance lease obligations	(12)	(12)
Other financing costs	(7)	(8)
Net cash (used in) provided by financing activities	(307)	0
Net (Decrease) Increase in Cash and Cash Equivalents, Including Assets Held for Sale	26	745
Decrease (Increase) in Cash and Cash Equivalents Included in Assets Held for Sale	0	2
Net (Decrease) Increase in Cash and Cash Equivalents	26	747
Cash and Cash Equivalents, Beginning of Period	161	247
Cash and Cash Equivalents, End of Period	187	994
Consumers Energy Company [Member]
Cash Flows from Operating Activities
Net income	198	245
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	299	282
Deferred income taxes and investment tax credit	39	82
Postretirement benefits expense	92	78
Other non-cash operating activities	31	31
Postretirement benefits contributions	(34)	(37)
Changes in other assets and liabilities:
Decrease (increase) in accounts receivable, notes receivable, and accrued revenue	146	207
Decrease (increase) in accrued power supply revenue		15
Decrease (increase) in inventories	137	202
Increase (decrease) in accounts payable	11	42
Increase (decrease) in accrued expenses	(19)	(12)
Decrease (increase) in other current and non-current assets	103	68
Increase (decrease) in other current and non-current liabilities	10	42
Net cash provided by operating activities	1,013	1,245
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(572)	(394)
Cost to retire property	(20)	(28)
Other investing activities	(9)	(23)
Net cash used in investing activities	(601)	(445)
Cash Flows from Financing Activities
Proceeds from issuance of long-term debt	375
Retirement of long-term debt	(694)	(18)
Payment of common stock dividends	(158)	(196)
Payment of preferred stock dividends	(1)	(1)
Stockholders contribution	150	125
Payment of capital and finance lease obligations	(12)	(12)
Other financing costs	(3)	(3)
Net cash (used in) provided by financing activities	(343)	(105)
Net (Decrease) Increase in Cash and Cash Equivalents	69	695
Cash and Cash Equivalents, Beginning of Period	85	71
Cash and Cash Equivalents, End of Period	$ 154	$ 766