Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current Assets
Cash and cash equivalents	$ 260	$ 93
Restricted cash and cash equivalents	32	29
Accounts receivable and accrued revenue, less allowances	678	855
Notes receivable	84	41
Accounts receivable - related parties	10	10
Accrued power supply and gas revenue	27	32
Inventories at average cost
Gas in underground storage	830	820
Materials and supplies	107	96
Generating plant fuel stock	152	168
Deferred property taxes	122	190
Regulatory assets	31	35
Prepayments and other current assets	68	53
Total current assets	2,401	2,422
Plant, Property, and Equipment
Plant, property, and equipment, gross	16,566	15,592
Less accumulated depreciation and amortization	5,355	5,121
Plant, property, and equipment, net	11,211	10,471
Construction work in progress	943	1,080
Total plant, property, and equipment	12,154	11,551
Other Non-current Assets
Regulatory assets, noncurrent	1,579	2,287
Accounts and notes receivable, less allowances	556	521
Investments	63	57
Other	233	293
Total other non-current assets	2,431	3,158
Total Assets	16,986	17,131
Current Liabilities
Current portion of long-term debt, capital and finance lease obligations	532	541
Notes payable		110
Accounts payable	519	512
Accounts payable - related parties	7	9
Accrued rate refunds		6
Accrued interest	65	95
Accrued taxes	88	279
Deferred income taxes	66	68
Regulatory liabilities, current	51	25
Other current liabilities	136	152
Total current liabilities	1,464	1,797
Non-current Liabilities
Long-term debt	7,089	6,710
Non-current portion of capital and finance lease obligations	140	153
Regulatory liabilities	2,086	2,101
Postretirement benefits	740	1,451
Asset retirement obligations	322	312
Deferred investment tax credit	41	43
Deferred income taxes	1,355	1,015
Other non-current liabilities	316	311
Total non-current liabilities	12,089	12,096
Commitments and Contingencies (Notes 1 and 2)
Equity
Common stock	3	3
Other paid-in capital	4,708	4,669
Accumulated other comprehensive loss	(39)	(55)
Retained earnings (Accumulated deficit)	(1,276)	(1,423)
Total common stockholders equity	3,396	3,194
Noncontrolling interests	37	44
Total equity	3,433	3,238
Total Liabilities and Equity	16,986	17,131
Consumers Energy Company [Member]
Current Assets
Cash and cash equivalents	199	5
Restricted cash and cash equivalents	31	28
Accounts receivable and accrued revenue, less allowances	669	844
Notes receivable	25
Accounts receivable - related parties	1	1
Accrued power supply and gas revenue	27	32
Inventories at average cost
Gas in underground storage	824	816
Materials and supplies	103	92
Generating plant fuel stock	152	167
Deferred property taxes	122	190
Regulatory assets	31	35
Prepayments and other current assets	60	45
Total current assets	2,244	2,255
Plant, Property, and Equipment
Plant, property, and equipment, gross	16,426	15,456
Less accumulated depreciation and amortization	5,292	5,061
Plant, property, and equipment, net	11,134	10,395
Construction work in progress	942	1,080
Total plant, property, and equipment	12,076	11,475
Other Non-current Assets
Regulatory assets, noncurrent	1,579	2,287
Accounts and notes receivable, less allowances	17	17
Investments	29	32
Other	149	209
Total other non-current assets	1,774	2,545
Total Assets	16,094	16,275
Current Liabilities
Current portion of long-term debt, capital and finance lease obligations	63	63
Notes payable		110
Accounts payable	508	501
Accounts payable - related parties	10	11
Accrued rate refunds		6
Accrued interest	43	65
Accrued taxes	201	376
Deferred income taxes	142	144
Regulatory liabilities, current	51	25
Other current liabilities	99	109
Total current liabilities	1,117	1,410
Non-current Liabilities
Long-term debt	4,591	4,297
Non-current portion of capital and finance lease obligations	140	153
Regulatory liabilities	2,086	2,101
Postretirement benefits	702	1,385
Asset retirement obligations	321	311
Deferred investment tax credit	41	43
Deferred income taxes	1,999	1,741
Other non-current liabilities	260	252
Total non-current liabilities	10,140	10,283
Commitments and Contingencies (Notes 1 and 2)
Equity
Common stock	841	841
Other paid-in capital	3,257	3,107
Accumulated other comprehensive loss	(9)	(8)
Retained earnings (Accumulated deficit)	711	598
Total common stockholders equity	4,800	4,538
Preferred stock	37	44
Total equity	4,837	4,582
Total Liabilities and Equity	$ 16,094	$ 16,275