Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities
Net Income	$ 462	$ 553	$ 525
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	881	811	750
Deferred income taxes and investment tax credit	417	264	247
Bad debt expense	49	50	58
Other non-cash operating activities and reconciling adjustments	82	52	100
Postretirement benefits contributions	(12)	(108)	(262)
Cash provided by (used in) changes in assets and liabilities
Decrease (increase) in accounts and notes receivable and accrued revenue	(66)	(155)	120
Decrease (increase) in inventories	(46)	146	147
Increase (decrease) in accounts payable and accrued refunds	49	59	(26)
Other current and non-current assets and liabilities	(111)	(43)	(19)
Net cash provided by operating activities	1,705	1,629	1,640
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(1,665)	(1,672)	(1,564)
Jackson plant acquisition			(154)
Decrease (increase) in EnerBank notes receivable	(138)	(136)	(279)
Proceeds from the sale of EnerBank notes receivable	50		48
Cost to retire property and other investing activities	(115)	(107)	(115)
Net cash used in investing activities	(1,868)	(1,915)	(2,064)
Cash Flows from Financing Activities
Proceeds from issuance of debt	1,633	1,049	599
Net increase in EnerBank certificates of deposit	47	100	214
Issuance of common stock	83	72	43
Retirement of debt	(980)	(728)	(224)
Debt prepayment costs	(22)	(18)
Payment of dividends on common and preferred stock	(377)	(347)	(322)
Change in notes payable	(228)	149	189
Payment of capital lease obligations and other financing costs	(46)	(22)	(36)
Net cash provided by (used in) financing activities	110	255	463
Net Increase (Decrease) in Cash and Cash Equivalents, Including Restricted Amounts	(53)	(31)	39
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	257	288	249
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	204	257	288
Cash transactions
Interest paid (net of amounts capitalized)	418	427	386
Income taxes paid (refunds received), net	5	32	10
Non-cash transactions
Capital expenditures not paid	172	138	201
Note receivable recorded for future refund of use taxes paid and capitalized		29
Other assets placed under capital lease	3	13	17
Consumers Energy Company [Member]
Cash Flows from Operating Activities
Net Income	632	616	594
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	872	803	744
Deferred income taxes and investment tax credit	163	289	204
Bad debt expense	29	31	50
Other non-cash operating activities and reconciling adjustments	59	25	98
Postretirement benefits contributions	(8)	(98)	(243)
Cash provided by (used in) changes in assets and liabilities
Decrease (increase) in accounts and notes receivable and accrued revenue	(63)	(138)	104
Decrease (increase) in inventories	(45)	145	144
Increase (decrease) in accounts payable and accrued refunds	43	57	(22)
Other current and non-current assets and liabilities	33	(49)	121
Net cash provided by operating activities	1,715	1,681	1,794
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under capital lease)	(1,632)	(1,656)	(1,537)
Jackson plant acquisition			(154)
Cost to retire property and other investing activities	(119)	(112)	(110)
Net cash used in investing activities	(1,751)	(1,768)	(1,801)
Cash Flows from Financing Activities
Proceeds from issuance of debt	834	446	250
Retirement of debt	(555)	(198)	(124)
Debt prepayment costs	(4)
Payment of dividends on common and preferred stock	(524)	(501)	(476)
Stockholder contribution	450	275	150
Change in notes payable	(228)	149	189
Payment of capital lease obligations and other financing costs	(24)	(3)	(23)
Net cash provided by (used in) financing activities	(51)	168	(34)
Net Increase (Decrease) in Cash and Cash Equivalents, Including Restricted Amounts	(87)	81	(41)
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	152	71	112
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	65	152	71
Cash transactions
Interest paid (net of amounts capitalized)	266	256	245
Income taxes paid (refunds received), net	(1)	50	(84)
Non-cash transactions
Capital expenditures not paid	160	127	182
Note receivable recorded for future refund of use taxes paid and capitalized		29
Other assets placed under capital lease	$ 3	$ 13	$ 17