Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets
Cash and cash equivalents	$ 128	$ 161
Restricted cash and cash equivalents	31	27
Accounts receivable and accrued revenue, less allowances	667	869
Notes receivable	28	49
Accounts receivable - related parties	11	10
Accrued power supply revenue	15
Inventories at average cost
Gas in underground storage	986	929
Materials and supplies	99	92
Generating plant fuel stock	187	166
Deferred income taxes		24
Deferred property taxes	119	187
Regulatory assets	27	1
Prepayments and other current assets	62	50
Total current assets	2,360	2,565
Plant, Property, and Equipment
Plant, property, and equipment, gross	15,103	14,751
Less accumulated depreciation and amortization	5,047	4,901
Plant, property, and equipment, net	10,056	9,850
Construction work in progress	1,134	783
Total plant, property, and equipment	11,190	10,633
Other Non-current Assets
Regulatory assets, noncurrent	2,273	2,466
Accounts and notes receivable, less allowances	512	462
Investments	56	50
Other	217	276
Total other non-current assets	3,058	3,254
Total Assets	16,608	16,452
Liabilities and Equity
Current portion of long-term debt, capital and finance lease obligations	510	1,057
Accounts payable	491	575
Accounts payable - related parties	9	9
Accrued rate refunds	17	30
Accrued interest	64	101
Accrued taxes	83	282
Deferred income taxes	52
Regulatory liabilities	122	125
Other current liabilities	137	159
Total current liabilities	1,485	2,338
Non-current Liabilities
Long-term debt	6,711	6,040
Non-current portion of capital and finance lease obligations	155	167
Regulatory liabilities	1,939	1,875
Postretirement benefits	1,291	1,289
Asset retirement obligations	264	254
Deferred investment tax credit	44	46
Deferred income taxes	1,156	1,035
Other non-current liabilities	323	336
Total non-current liabilities	11,883	11,042
Commitments and Contingencies (Notes 3, 4, 5, 7, and 8)
Equity
Common stock	3	3
Other paid-in capital	4,662	4,627
Accumulated other comprehensive loss	(43)	(49)
Retained earnings (Accumulated deficit)	(1,426)	(1,553)
Total common stockholders equity	3,196	3,028
Noncontrolling interests	44	44
Total equity	3,240	3,072
Total Liabilities and Equity	16,608	16,452
Consumers Energy Company [Member]
Assets
Cash and cash equivalents	57	85
Restricted cash and cash equivalents	30	26
Accounts receivable and accrued revenue, less allowances	659	860
Notes receivable		23
Accounts receivable - related parties	1	1
Accrued power supply revenue	15
Inventories at average cost
Gas in underground storage	982	929
Materials and supplies	95	88
Generating plant fuel stock	186	164
Deferred property taxes	119	187
Regulatory assets	27	1
Prepayments and other current assets	56	43
Total current assets	2,227	2,407
Plant, Property, and Equipment
Plant, property, and equipment, gross	14,968	14,621
Less accumulated depreciation and amortization	4,988	4,846
Plant, property, and equipment, net	9,980	9,775
Construction work in progress	1,133	782
Total plant, property, and equipment	11,113	10,557
Other Non-current Assets
Regulatory assets, noncurrent	2,273	2,466
Accounts and notes receivable, less allowances	26	1
Investments	31	35
Other	134	196
Total other non-current assets	2,464	2,698
Total Assets	15,804	15,662
Liabilities and Equity
Current portion of long-term debt, capital and finance lease obligations	62	363
Accounts payable	480	561
Accounts payable - related parties	11	11
Accrued rate refunds	17	30
Accrued interest	34	73
Accrued taxes	198	287
Deferred income taxes	101	73
Regulatory liabilities	122	125
Other current liabilities	105	119
Total current liabilities	1,130	1,642
Non-current Liabilities
Long-term debt	4,308	3,987
Non-current portion of capital and finance lease obligations	155	167
Regulatory liabilities	1,939	1,875
Postretirement benefits	1,229	1,225
Asset retirement obligations	263	253
Deferred investment tax credit	44	46
Deferred income taxes	1,881	1,817
Other non-current liabilities	252	256
Total non-current liabilities	10,071	9,626
Commitments and Contingencies (Notes 3, 4, 5, 7, and 8)
Equity
Common stock	841	841
Other paid-in capital	3,107	2,957
Accumulated other comprehensive loss		(2)
Retained earnings (Accumulated deficit)	611	554
Total common stockholders equity	4,559	4,350
Preferred stock	44	44
Total equity	4,603	4,394
Total Liabilities and Equity	$ 15,804	$ 15,662