Contingencies And Commitments (Contingencies And Commitments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended										1 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Oct. 31, 2010	Mar. 31, 2013 Consumers Energy Company [Member]	Dec. 31, 2012 Consumers Energy Company [Member]	Mar. 31, 2013 NREPA [Member] Consumers Energy Company [Member]	Mar. 31, 2013 Superfund Liability [Member] Consumers Energy Company [Member]	Mar. 31, 2013 Manufactured Gas Plant [Member] Consumers Energy Company [Member] item	Mar. 31, 2013 Big Rock Decommissioning [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Big Rock Decommissioning [Member] Consumers Energy Company [Member]	Jul. 31, 2011 DOE Settlement [Member] Consumers Energy Company [Member]
Demand for payment by USEPA			$ 7
Cumulative environmental charge	227
Recorded liability	60							122
Discounted projected costs rate	4.34%							2.57%
Site contingency accrual inflation rate	1.00%							2.50%
Remaining undiscounted obligation amount	78							132
Foreign government tax claim on sale	142
Remediation and other response activity costs, minimum						4	2
Remediation and other response activity costs. maximum						6	8
Accrual for environmental loss contingencies						4	2
Litigation settlement, gross											120
Amount Paid to Transfer Ownership and Responsibility									30	30
Number of former MGPs								23
Regulatory assets, noncurrent	$ 2,223	$ 2,287		$ 2,223	$ 2,287			$ 151		$ 85