Stock-Based Compensation (Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Grants In Period, Weighted Average Grant Date Fair Value) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-Average Grant Date Fair Value per Share, Granted	$ 28.61	$ 31.74	$ 36.84
Restricted Stock [Member] | Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-Average Grant Date Fair Value per Share, Granted	28.67	31.77	36.83
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-Average Grant Date Fair Value per Share, Granted	41.98	39.12	34.25
Restricted Stock Units (RSUs) [Member] | Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-Average Grant Date Fair Value per Share, Granted	$ 41.97	$ 39.12	$ 34.25