Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current Assets
Cash and cash equivalents	$ 537	$ 93
Restricted cash and cash equivalents	29	29
Accounts receivable and accrued revenue, less allowances	728	855
Notes receivable	76	41
Accounts receivable - related parties	10	10
Accrued power supply and gas revenue	20	32
Inventories at average cost
Gas in underground storage	568	820
Materials and supplies	103	96
Generating plant fuel stock	159	168
Deferred property taxes	140	190
Regulatory assets	36	35
Prepayments and other current assets	79	53
Total current assets	2,485	2,422
Plant, Property, and Equipment
Plant, property, and equipment, gross	16,086	15,592
Less accumulated depreciation and amortization	5,278	5,121
Plant, property, and equipment, net	10,808	10,471
Construction work in progress	1,108	1,080
Total plant, property, and equipment	11,916	11,551
Other Non-current Assets
Regulatory assets, noncurrent	2,202	2,287
Accounts and notes receivable, less allowances	504	521
Investments	63	57
Other	259	293
Total other non-current assets	3,028	3,158
Total Assets	17,429	17,131
Current Liabilities
Current portion of long-term debt, capital and finance lease obligations	758	541
Notes payable		110
Accounts payable	512	512
Accounts payable - related parties	9	9
Accrued rate refunds		6
Accrued interest	93	95
Accrued taxes	206	279
Deferred income taxes	77	68
Regulatory liabilities, current	8	25
Other current liabilities	139	152
Total current liabilities	1,802	1,797
Non-current Liabilities
Long-term debt	6,695	6,710
Non-current portion of capital and finance lease obligations	144	153
Regulatory liabilities	2,243	2,101
Postretirement benefits	1,393	1,451
Asset retirement obligations	319	312
Deferred investment tax credit	41	43
Deferred income taxes	1,116	1,015
Other non-current liabilities	316	311
Total non-current liabilities	12,267	12,096
Commitments and Contingencies (Notes 1 and 2)
Equity
Common stock	3	3
Other paid-in capital	4,710	4,669
Accumulated other comprehensive loss	(56)	(55)
Retained earnings (Accumulated deficit)	(1,334)	(1,423)
Total common stockholders equity	3,323	3,194
Noncontrolling interests	37	44
Total equity	3,360	3,238
Total Liabilities and Equity	17,429	17,131
Consumers Energy Company [Member]
Current Assets
Cash and cash equivalents	286	5
Restricted cash and cash equivalents	28	28
Accounts receivable and accrued revenue, less allowances	719	844
Notes receivable	25
Accounts receivable - related parties	1	1
Accrued power supply and gas revenue	20	32
Inventories at average cost
Gas in underground storage	568	816
Materials and supplies	99	92
Generating plant fuel stock	159	167
Deferred property taxes	140	190
Regulatory assets	36	35
Prepayments and other current assets	72	45
Total current assets	2,153	2,255
Plant, Property, and Equipment
Plant, property, and equipment, gross	15,951	15,456
Less accumulated depreciation and amortization	5,216	5,061
Plant, property, and equipment, net	10,735	10,395
Construction work in progress	1,106	1,080
Total plant, property, and equipment	11,841	11,475
Other Non-current Assets
Regulatory assets, noncurrent	2,202	2,287
Accounts and notes receivable, less allowances	11	17
Investments	30	32
Other	172	209
Total other non-current assets	2,415	2,545
Total Assets	16,409	16,275
Current Liabilities
Current portion of long-term debt, capital and finance lease obligations	63	63
Notes payable		110
Accounts payable	502	501
Accounts payable - related parties	13	11
Accrued rate refunds		6
Accrued interest	59	65
Accrued taxes	316	376
Deferred income taxes	127	144
Regulatory liabilities, current	8	25
Other current liabilities	100	109
Total current liabilities	1,188	1,410
Non-current Liabilities
Long-term debt	4,276	4,297
Non-current portion of capital and finance lease obligations	144	153
Regulatory liabilities	2,243	2,101
Postretirement benefits	1,329	1,385
Asset retirement obligations	318	311
Deferred investment tax credit	41	43
Deferred income taxes	1,820	1,741
Other non-current liabilities	259	252
Total non-current liabilities	10,430	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)	665	598
Total common stockholders equity	4,754	4,538
Preferred stock	37	44
Total equity	4,791	4,582
Total Liabilities and Equity	$ 16,409	$ 16,275