Leases (Schedule of Future Minimum Lease Payments for Leases) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Capital Leases Future Minimum Payments Due Current	$ 14
Capital Leases Future Minimum Payments Due In Two Years	13
Capital Leases Future Minimum Payments Due In Three Years	14
Capital Leases Future Minimum Payments Due In Four Years	10
Capital Leases Future Minimum Payments Due In Five Years	9
Capital Leases Future Minimum Payments Due Thereafter	36
Capital Leases, Future Minimum Payments Due, Total	96
Capital Leases Future Minimum Payments Interest Included In Payments	43
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Total	53
Capital Leases Future Minimum Payments Present Value Of Net Minimum Payments, Current Portion	9
Capital Leases Future Minimum Payments Present Value Of Net Minimum Payments NonCurrent Portion	44
Finance Leases Future Minimum Payments Due Current	20
Finance Leases Future Minimum Payments Due In Two Years	19
Finance Leases Future Minimum Payments Due In Three Years	18
Finance Leases Future Minimum Payments Due In Four Years	17
Finance Leases Future Minimum Payments Due In Five Years	17
Finance Leases Future Minimum Payments Due Thereafter	62
Finance Leases Future Minimum Payments Due	153
Finance Leases Future Minimum Payments Interest Included In Payments	31
Finance Leases Future Minimum Payments Present Value Of Net Minimum Payments	122
Finance Leases Future Minimum Payments Present Value Of Net Minimum Payments, Current Portion	13
Finance Leases Future Minimum Payments Present Value Of Net Minimum Payments, Non Current Portion	109
Operating Leases Future Minimum Payments Due Current	26
Operating Leases Future Minimum Payments Due In Two Years	25
Operating Leases Future Minimum Payments Due In Three Years	24
Operating Leases Future Minimum Payments Due In Four Years	19
Operating Leases Future Minimum Payments Due In Five Years	19
Operating Leases Future Minimum Payments Due Thereafter	67
Operating Leases, Future Minimum Payments Due, Total	180
Finance Leases Lessee Balance Sheet Assets Amortization And Interest Charges	20	21	22
Consumers Energy Company [Member]
Capital Leases Future Minimum Payments Due Current	14
Capital Leases Future Minimum Payments Due In Two Years	13
Capital Leases Future Minimum Payments Due In Three Years	14
Capital Leases Future Minimum Payments Due In Four Years	10
Capital Leases Future Minimum Payments Due In Five Years	9
Capital Leases Future Minimum Payments Due Thereafter	36
Capital Leases, Future Minimum Payments Due, Total	96
Capital Leases Future Minimum Payments Interest Included In Payments	43
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments, Total	53
Capital Leases Future Minimum Payments Present Value Of Net Minimum Payments, Current Portion	9
Capital Leases Future Minimum Payments Present Value Of Net Minimum Payments NonCurrent Portion	44
Finance Leases Future Minimum Payments Due Current	20
Finance Leases Future Minimum Payments Due In Two Years	19
Finance Leases Future Minimum Payments Due In Three Years	18
Finance Leases Future Minimum Payments Due In Four Years	17
Finance Leases Future Minimum Payments Due In Five Years	17
Finance Leases Future Minimum Payments Due Thereafter	62
Finance Leases Future Minimum Payments Due	153
Finance Leases Future Minimum Payments Interest Included In Payments	31
Finance Leases Future Minimum Payments Present Value Of Net Minimum Payments	122
Finance Leases Future Minimum Payments Present Value Of Net Minimum Payments, Current Portion	13
Finance Leases Future Minimum Payments Present Value Of Net Minimum Payments, Non Current Portion	109
Operating Leases Future Minimum Payments Due Current	26
Operating Leases Future Minimum Payments Due In Two Years	25
Operating Leases Future Minimum Payments Due In Three Years	24
Operating Leases Future Minimum Payments Due In Four Years	19
Operating Leases Future Minimum Payments Due In Five Years	19
Operating Leases Future Minimum Payments Due Thereafter	67
Operating Leases, Future Minimum Payments Due, Total	180
Finance Lease Term	15 years
Finance Leases Lessee Balance Sheet Assets Amortization And Interest Charges	$ 20	$ 21	$ 22