Leases (Components of Lease Cost) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 10	$ 31
Finance lease cost:
Amortization of right-of-use assets	0	3
Interest of lease liabilities	0	0
Total finance lease cost	0	3
Variable lease cost	2	8
Short-term lease cost	2	7
Total lease cost	14	49
DTE Electric
Lessee, Lease, Description [Line Items]
Operating lease cost	5	13
Finance lease cost:
Amortization of right-of-use assets	0	3
Interest of lease liabilities	0	0
Total finance lease cost	0	3
Variable lease cost	0	0
Short-term lease cost	1	2
Total lease cost	$ 6	$ 18