Retirement Benefits and Trusteed Assets (OPEB - Postretirement Cost Inclusions) (Details) - Other postretirement benefit plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 26	$ 22	$ 27
Interest cost	56	70	69
Expected return on plan assets	(128)	(96)	(143)
Amortization of:
Net actuarial loss	16	12	11
Prior service credit	(19)	(9)	0
Net pension cost/other postretirement cost (credit)	(49)	(1)	(36)
DTE Electric
Defined Benefit Plan Disclosure [Line Items]
Service cost	20	16	20
Interest cost	43	53	53
Expected return on plan assets	(87)	(65)	(98)
Amortization of:
Net actuarial loss	11	5	8
Prior service credit	(14)	(7)	0
Net pension cost/other postretirement cost (credit)	$ (27)	$ 2	$ (17)