Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities
Net Income	$ 752	$ 682	$ 659
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	1,048	992	933
Deferred income taxes and investment tax credits	170	150	182
Bad debt expense	90	67	54
Other non‑cash operating activities and reconciling adjustments	(22)	(58)	22
Postretirement benefits contributions	(712)	(10)	(252)
Cash provided by (used in) changes in assets and liabilities
Accounts and notes receivable and accrued revenue	(12)	45	15
Inventories	28	44	14
Accounts payable and accrued rate refunds	54	(69)	22
Other current and non‑current assets and liabilities	(120)	(53)	54
Net cash provided by operating activities	1,276	1,790	1,703
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under finance lease)	(2,317)	(2,104)	(2,074)
Increase in EnerBank notes receivable	(657)	(401)	(307)
Purchase of notes receivable by EnerBank	(17)	(343)	(225)
Proceeds from DB SERP investments	0	0	146
Proceeds from sale of EnerBank notes receivable	197	67	0
Proceeds from sale of transmission equipment	58	97	0
Cost to retire property and other investing activities	(131)	(132)	(146)
Net cash used in investing activities	(2,867)	(2,816)	(2,606)
Cash Flows from Financing Activities
Proceeds from issuance of debt	3,179	2,151	2,767
Retirement of debt	(2,010)	(1,285)	(1,870)
Increase in EnerBank certificates of deposit	416	631	513
Decrease in notes payable	(90)	(7)	(73)
Issuance of common stock, net of issuance costs	253	12	41
Payment of dividends on common and preferred stock	(467)	(436)	(407)
Debt prepayment costs	(59)	(8)	(36)
Proceeds from the sale of membership interest in VIE to tax equity investor	417	0	0
Contribution from noncontrolling interest	31	0	0
Other financing costs	(51)	(50)	(61)
Net cash provided by financing activities	1,619	1,008	874
Net Increase (Decrease) in Cash and Cash Equivalents, Including Restricted Amounts	28	(18)	(29)
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	157	175	204
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	185	157	175
Cash transactions
Interest paid (net of amounts capitalized)	549	498	458
Income taxes paid (refunds received), net	(58)	(58)	(123)
Non‑cash transactions
Capital expenditures not paid	141	170	158
Consumers Energy Company
Cash Flows from Operating Activities
Net Income	816	743	705
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	1,023	975	921
Deferred income taxes and investment tax credits	177	37	123
Bad debt expense			29
Other non‑cash operating activities and reconciling adjustments	(30)	(32)	13
Postretirement benefits contributions	(690)	(7)	(242)
Cash provided by (used in) changes in assets and liabilities
Accounts and notes receivable and accrued revenue	(46)	8	(26)
Inventories	26	40	15
Accounts payable and accrued rate refunds	45	(63)	12
Other current and non‑current assets and liabilities	(136)	(129)	(101)
Net cash provided by operating activities	1,218	1,601	1,449
Cash Flows from Investing Activities
Capital expenditures (excludes assets placed under finance lease)	(2,170)	(2,085)	(1,822)
Proceeds from DB SERP investments	0	0	106
DB SERP investment in note receivable – related party	(5)	0	(106)
Proceeds from sale of transmission equipment	58	77	0
Cost to retire property and other investing activities	(129)	(129)	(149)
Net cash used in investing activities	(2,246)	(2,137)	(1,971)
Cash Flows from Financing Activities
Proceeds from issuance of debt	1,954	993	2,106
Retirement of debt	(1,086)	(541)	(1,193)
Decrease in notes payable	(90)	(7)	(73)
Increase in notes payable – related parties	307	0	0
Stockholder contribution	650	675	250
Payment of dividends on common and preferred stock	(639)	(594)	(533)
Debt prepayment costs	(43)	(8)	(20)
Other financing costs	(18)	(10)	(24)
Net cash provided by financing activities	1,035	508	513
Net Increase (Decrease) in Cash and Cash Equivalents, Including Restricted Amounts	7	(28)	(9)
Cash and Cash Equivalents, Including Restricted Amounts, Beginning of Period	28	56	65
Cash and Cash Equivalents, Including Restricted Amounts, End of Period	35	28	56
Cash transactions
Interest paid (net of amounts capitalized)	305	279	287
Income taxes paid (refunds received), net	51	132	156
Non‑cash transactions
Capital expenditures not paid	$ 130	$ 160	$ 143