Debt (Capital Lease Obligations) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Minimum Lease Payments, Sale Leaseback Transactions, Fiscal Year Maturity [Abstract]
Minimum Lease Payments, Sale Leaseback Transactions, within One Year	$ 21	[1]
Minimum Lease Payments, Sale Leaseback Transactions, within Two Years	21	[1]
Minimum Lease Payments, Sale Leaseback Transactions, within Three Years	21	[1]
Minimum Lease Payments, Sale Leaseback Transactions, within Four Years	16	[1]
Minimum Lease Payments, Sale Leaseback Transactions, within Five Years	6	[1]
Minimum Lease Payments, Sale Leaseback Transactions, Thereafter	20	[1]
Minimum Lease Payments, Sale Leaseback Transactions	105	[1]
Interest Portion of Minimum Lease Payments, Sale Leaseback Transactions	29	[1]
Present Value of Future Minimum Lease Payments, Sale Leaseback Transactions	76	[1]
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Capital Leases, Future Minimum Payments Due, Current	19
Capital Leases, Future Minimum Payments Due in Two Years	19
Capital Leases, Future Minimum Payments Due in Three Years	17
Capital Leases, Future Minimum Payments Due in Four Years	17
Capital Leases, Future Minimum Payments Due in Five Years	21
Capital Leases, Future Minimum Payments Due Thereafter	72
Capital Leases, Future Minimum Payments Due	165
Capital Leases, Future Minimum Payments, Interest Included in Payments	60
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	105
Total Leases Future Minimum Payments [Abstract]
Total Leases, Future Minimum Payments Due, Current	40
Total Leases, Future Minimum Payments Due in Two Years	40
Total Leases, Future Minimum Payments Due in Three Years	38
Total Leases, Future Minimum Payments Due in Four Years	33
Total Leases, Future Minimum Payments Due in Five Years	27
Total Leases, Future Minimum Payments Due Thereafter	92
Total Leases, Future Minimum Payments Due	270
Total Leases, Future Minimum Payments, Interest Included in Payments	89
Total Leases, Future Minimum Payments, Present Value of Net Minimum Payments	$ 181

[1] Amounts are accounted for as a financing transaction under U.S. GAAP and are included in our project financing, notes payable and other amounts above.