Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Leases [Abstract]
Capital Leased Assets, Gross	$ 57
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation	8
Capital Lease Obligations, Current	2
Purchase Commitment, Remaining Minimum Amount Committed	47
Deferred Costs, Leasing, Accumulated Amortization		$ 3
Interest Expense, Lessee, Assets under Capital Lease		$ 4
Long-term Purchase Commitment, Amount	149
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	131
Operating Leases, Rent Expense	7
Operating Leases, Rent Expense, Contingent Rentals	14
Operating Leases, Rent Expense, Sublease Rentals	$ 4