Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current Assets
Cash and cash equivalents	$ 586	$ 93
Restricted cash and cash equivalents	29	29
Accounts receivable and accrued revenue, less allowances	914	855
Notes receivable	73	41
Accounts receivable - related parties	10	10
Accrued power supply and gas revenue	28	32
Inventories at average cost
Gas in underground storage	389	820
Materials and supplies	99	96
Generating plant fuel stock	149	168
Deferred property taxes	157	190
Regulatory assets	38	35
Prepayments and other current assets	56	53
Total current assets	2,528	2,422
Plant, Property, and Equipment
Plant, property, and equipment, gross	15,732	15,592
Less accumulated depreciation and amortization	5,200	5,121
Plant, property, and equipment, net	10,532	10,471
Construction work in progress	1,135	1,080
Total plant, property, and equipment	11,667	11,551
Other Non-current Assets
Regulatory assets, noncurrent	2,223	2,287
Accounts and notes receivable, less allowances	508	521
Investments	60	57
Other	283	293
Total other non-current assets	3,074	3,158
Total Assets	17,269	17,131
Current Liabilities
Current portion of long-term debt, capital and finance lease obligations	732	541
Notes payable		110
Accounts payable	426	512
Accounts payable - related parties	10	9
Accrued rate refunds	1	6
Accrued interest	68	95
Accrued taxes	211	279
Deferred income taxes	49	68
Regulatory liabilities, current	14	25
Other current liabilities	134	152
Total current liabilities	1,645	1,797
Non-current Liabilities
Long-term debt	6,741	6,710
Non-current portion of capital and finance lease obligations	149	153
Regulatory liabilities	2,219	2,101
Postretirement benefits	1,398	1,451
Asset retirement obligations	316	312
Deferred investment tax credit	42	43
Deferred income taxes	1,098	1,015
Other non-current liabilities	311	311
Total non-current liabilities	12,274	12,096
Commitments and Contingencies (Notes 1 and 2)
Equity
Common stock	3	3
Other paid-in capital	4,703	4,669
Accumulated other comprehensive loss	(54)	(55)
Retained earnings (Accumulated deficit)	(1,346)	(1,423)
Total common stockholders equity	3,306	3,194
Noncontrolling interests	44	44
Total equity	3,350	3,238
Total Liabilities and Equity	17,269	17,131
Consumers Energy Company [Member]
Current Assets
Cash and cash equivalents	355	5
Restricted cash and cash equivalents	28	28
Accounts receivable and accrued revenue, less allowances	901	844
Notes receivable	25
Accounts receivable - related parties	2	1
Accrued power supply and gas revenue	28	32
Inventories at average cost
Gas in underground storage	389	816
Materials and supplies	95	92
Generating plant fuel stock	148	167
Deferred property taxes	157	190
Regulatory assets	38	35
Prepayments and other current assets	50	45
Total current assets	2,216	2,255
Plant, Property, and Equipment
Plant, property, and equipment, gross	15,596	15,456
Less accumulated depreciation and amortization	5,139	5,061
Plant, property, and equipment, net	10,457	10,395
Construction work in progress	1,134	1,080
Total plant, property, and equipment	11,591	11,475
Other Non-current Assets
Regulatory assets, noncurrent	2,223	2,287
Accounts and notes receivable, less allowances	14	17
Investments	30	32
Other	198	209
Total other non-current assets	2,465	2,545
Total Assets	16,272	16,275
Current Liabilities
Current portion of long-term debt, capital and finance lease obligations	262	63
Notes payable		110
Accounts payable	414	501
Accounts payable - related parties	14	11
Accrued rate refunds	1	6
Accrued interest	37	65
Accrued taxes	329	376
Deferred income taxes	118	144
Regulatory liabilities, current	14	25
Other current liabilities	97	109
Total current liabilities	1,286	1,410
Non-current Liabilities
Long-term debt	4,086	4,297
Non-current portion of capital and finance lease obligations	149	153
Regulatory liabilities	2,219	2,101
Postretirement benefits	1,334	1,385
Asset retirement obligations	315	311
Deferred investment tax credit	42	43
Deferred income taxes	1,785	1,741
Other non-current liabilities	253	252
Total non-current liabilities	10,183	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	(6)	(8)
Retained earnings (Accumulated deficit)	667	598
Total common stockholders equity	4,759	4,538
Preferred stock	44	44
Total equity	4,803	4,582
Total Liabilities and Equity	$ 16,272	$ 16,275