Retirement Benefits and Trusteed Assets (OPEB - Accumulated Postretirement Obligations in Excess of Plan Assets) (Details) - Other postretirement benefit plan - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Accumulated postretirement benefit obligation	$ 878	$ 840
Fair value of plan assets	470	454
Accumulated postretirement benefit obligation in excess of plan assets	408	386
DTE Electric
Defined Benefit Plan Disclosure [Line Items]
Accumulated postretirement benefit obligation	826	795
Fair value of plan assets	442	428
Accumulated postretirement benefit obligation in excess of plan assets	$ 384	$ 367