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Retirement Benefits and Trusteed Assets (OPEB - Accumulated Postretirement Obligations in Excess of Plan Assets) (Details) - Other postretirement benefit plan - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]    
Accumulated postretirement benefit obligation $ 822 $ 878
Fair value of plan assets 463 470
Accumulated postretirement benefit obligation in excess of plan assets 359 408
DTE Electric    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated postretirement benefit obligation 775 826
Fair value of plan assets 435 442
Accumulated postretirement benefit obligation in excess of plan assets $ 340 $ 384