Leases Leases (Details Textuals) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) agreement	Dec. 31, 2018 USD ($) agreement	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Lessee, Lease, Description [Line Items]
Short-term leases expense	$ 2
Term of finance lease contract	20 years
Finance lease contract, renewal option extension term	5 years
Percent ownership interest in Vector Pipeline	40.00%
Number of energy services agreements | agreement	2
Depreciation expense associated with property under operating leases	$ 8
Interest income recognized under finance leases	$ 1
Contingent rental revenues		$ 107	$ 91	$ 101
Pipeline System Lease
Lessee, Lease, Description [Line Items]
Percent ownership interest in Vector Pipeline		40.00%
Number of energy services agreements | agreement		2
Lessor capital lease renewal terms		5 years
Minimum
Lessee, Lease, Description [Line Items]
Lease terms	2 years
Term of operating lease contracts	3 years
Maximum
Lessee, Lease, Description [Line Items]
Lease terms	40 years
Term of operating lease contracts	24 years
DTE Electric
Lessee, Lease, Description [Line Items]
Short-term leases expense	$ 1
DTE Electric | Minimum
Lessee, Lease, Description [Line Items]
Lease terms	2 years
DTE Electric | Maximum
Lessee, Lease, Description [Line Items]
Lease terms	40 years