Significant Accounting Policies (Roll-Forward of Activity for Financing Receivables Credit Loss Reserves) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Jan. 01, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 104	$ 83
Current period provision	42	105
Write-offs charged against allowance	(93)	(134)
Recoveries of amounts previously written off	49	50
Ending balance	102	104
DTE Electric
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	57	46
Current period provision	27	61
Write-offs charged against allowance	(58)	(80)
Recoveries of amounts previously written off	29	30
Ending balance	55	57
Trade accounts receivable
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	101	79
Current period provision	41	102
Write-offs charged against allowance	(92)	(130)
Recoveries of amounts previously written off	49	50
Ending balance	99	101
Trade accounts receivable | Discontinued operations, spinoff | DT Midstream
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Trade accounts receivable reserve related to discontinued operations			$ 8
Other receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3	4
Current period provision	1	3
Write-offs charged against allowance	(1)	(4)
Recoveries of amounts previously written off	0	0
Ending balance	$ 3	$ 3