Retirement Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Reduced regulatory income tax liabilities	$ 86	$ 131
Increased income tax expense	302	245	191
Union employees percentage	43.00%
CMS Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Increased income tax expense	(50)	(62)	(61)
Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Reduced regulatory income tax liabilities	86	131
Increased income tax expense	346	297	267
Union employees percentage	45.00%
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Trust assets	1,964	1,727	1,626
Amortization of net actuarial loss from regulatory asset	57
Amortization of net actuarial loss, net of tax	2
Estimated time of amortization of gains losses	10 years	11 years	11 years
Investment grade bonds included in the corporate debt investments category of the plan trust assets		68.00%
High-yield bonds included in the corporate debt investments category of the Plan trust assets		32.00%
U.S. equity securities included in the Pooled funds category of the Plan trust assets	61.00%	51.00%
Foreign equity securities included in the Pooled funds category of the Plan trust assets	28.00%	26.00%
Foreign fixed-income securities included in the Pooled funds category of the Plan trust assets	3.00%	14.00%
U.S. fixed-income securities included in the Pooled funds category of the Plan trust assets	4.00%	4.00%
Alternative investments included in the Pooled funds category of the Plan trust assets	4.00%	5.00%
Pension [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortization of net actuarial loss from regulatory asset	57
Estimated time of amortization of gains losses	10 years	11 years	11 years
401 (K) Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer match of eligible contributions	60.00%	60.00%	60.00%
Employer match of eligible wages	6.00%	6.00%	6.00%
Savings plan, cost recognized	17	16	16
401 (K) Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer match of eligible contributions	60.00%	60.00%	60.00%
Employer match of eligible wages	6.00%	6.00%	6.00%
Savings plan, cost recognized	17	16	16
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Trust assets	1,218	1,047	924
Retirement age requirement	55	55	55
Retirement years of service	10 years	10 years	10 years
Retirement years of service with disability	15 years	15 years	15 years
Ultimate health care cost trend rate	4.75%
Year that rate reaches ultimate trend rate	2024
Amortization of net prior service cost (credit) from regulatory liability	37
Amortization of net prior service cost (credit) from AOCI	(1)
Estimated time of amortization of gains losses	13 years	13 years	13 years
Estimated time of prior service cost	10 years
Investment grade bonds included in the corporate debt investments category of the plan trust assets		68.00%
High-yield bonds included in the corporate debt investments category of the Plan trust assets		32.00%
U.S. equity securities included in the Pooled funds category of the Plan trust assets	60.00%	65.00%
Foreign equity securities included in the Pooled funds category of the Plan trust assets	20.00%	21.00%
Foreign fixed-income securities included in the Pooled funds category of the Plan trust assets	4.00%	9.00%
U.S. fixed-income securities included in the Pooled funds category of the Plan trust assets	14.00%	3.00%
Alternative investments included in the Pooled funds category of the Plan trust assets	2.00%	2.00%
OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Trust assets	1,141	978	861
Retirement age requirement	55	55	55
Retirement years of service	10 years	10 years	10 years
Retirement years of service with disability	15 years	15 years	15 years
Ultimate health care cost trend rate	4.75%
Year that rate reaches ultimate trend rate	2024
Amortization of net prior service cost (credit) from regulatory liability	37
Estimated time of amortization of gains losses	13 years	13 years	13 years
Estimated time of prior service cost	10 years
Investment grade bonds included in the corporate debt investments category of the plan trust assets		68.00%
High-yield bonds included in the corporate debt investments category of the Plan trust assets		32.00%
U.S. equity securities included in the Pooled funds category of the Plan trust assets	60.00%	65.00%
Foreign equity securities included in the Pooled funds category of the Plan trust assets	20.00%	21.00%
Foreign fixed-income securities included in the Pooled funds category of the Plan trust assets	4.00%	9.00%
U.S. fixed-income securities included in the Pooled funds category of the Plan trust assets	14.00%	3.00%
Alternative investments included in the Pooled funds category of the Plan trust assets	2.00%	2.00%
Pension And OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortized net gains and losses in excess of PBO or MRV	10.00%	10.00%	10.00%
Pension And OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Amortized net gains and losses in excess of PBO or MRV	10.00%	10.00%	10.00%
Defined Company Contribution Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contribution, percentage of base pay	6.00%	6.00%	6.00%
Plan cost, defined contribution plan	10	8	7
Defined Company Contribution Plan [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contribution, percentage of base pay	6.00%	6.00%	6.00%
Plan cost, defined contribution plan	10	8	7
DC SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Minimum years of participation before vesting	5 years
Trust assets	1	1
DC SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Minimum years of participation before vesting	5 years
Trust assets	1	1
Minimum [Member] | DC SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan contribution percentage	5.00%
Minimum [Member] | DC SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan contribution percentage	5.00%
Maximum [Member] | DC SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan cost, defined contribution plan	1	1	1
Plan contribution percentage	15.00%
Maximum [Member] | DC SERP [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan cost, defined contribution plan	1	1	1
Plan contribution percentage	15.00%
Under Age 65 [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate assumed for next fiscal year	6.50%	8.00%
Under Age 65 [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate assumed for next fiscal year	6.50%	8.00%
Over Age 65 [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate assumed for next fiscal year	6.50%	7.50%
Over Age 65 [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate assumed for next fiscal year	6.50%	7.50%
Remeasurement As Of July 1, 2013 [Member] | OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Deacrease in liability	638
Regulatory asset decrease	580
Increase in regulatory liabilities	34
Decrease in AOCL	24
Decrease deferred tax assets	148
Reduced regulatory income tax liabilities	144
Increased income tax expense	4
Remeasurement As Of July 1, 2013 [Member] | OPEB [Member] | Consumers Energy Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Deacrease in liability	614
Regulatory asset decrease	580
Increase in regulatory liabilities	34
Decrease deferred tax assets	144
Reduced regulatory income tax liabilities	$ 144