Retirement Benefits and Trusteed Assets (OPEB - Postretirement Cost Inclusions) (Details) - Other postretirement benefit plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 27	$ 27	$ 34
Interest cost	73	80	81
Expected return on plan assets	(130)	(129)	(131)
Amortization of:
Net actuarial loss	13	30	43
Prior service cost	(14)	(118)	(126)
Other	0	(1)	0
Net pension cost	(31)	(111)	(99)
DTE Electric
Defined Benefit Plan Disclosure [Line Items]
Service cost	20	20	25
Interest cost	56	61	62
Expected return on plan assets	(90)	(90)	(90)
Amortization of:
Net actuarial loss	8	21	31
Prior service cost	(10)	(89)	(95)
Net pension cost	$ (16)	$ (77)	$ (67)