Significant Accounting Policies (Financing Receivables Classified by Internal Grade of Credit Risk) (Details) $ in Millions	Sep. 30, 2021 USD ($)
Notes receivable
Financing Receivable, Credit Quality Indicator [Line Items]
2021	$ 2
2020	100
2019 and Prior	40
Total	142
Notes receivable | DTE Electric
Financing Receivable, Credit Quality Indicator [Line Items]
Total	17
Notes receivable | Internal grade 1
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019 and Prior	19
Total	19
Notes receivable | Internal grade 1 | DTE Electric
Financing Receivable, Credit Quality Indicator [Line Items]
Total	14
Notes receivable | Internal grade 2
Financing Receivable, Credit Quality Indicator [Line Items]
2021	2
2020	100
2019 and Prior	21
Total	123
Notes receivable | Internal grade 2 | DTE Electric
Financing Receivable, Credit Quality Indicator [Line Items]
Total	3
Notes receivable | Internal grade 3
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	0
2019 and Prior	0
Total	0
Notes receivable | Internal grade 3 | DTE Electric
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0
Net investment in leases
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	161
2019 and Prior	40
Total	201
Net investment in leases | DTE Electric
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0
Net investment in leases | Internal grade 1
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	2
2019 and Prior	39
Total	41
Net investment in leases | Internal grade 1 | DTE Electric
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0
Net investment in leases | Internal grade 2
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	159
2019 and Prior	1
Total	160
Net investment in leases | Internal grade 2 | DTE Electric
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 0