Summary of Significant Accounting Policies Contractual Future Minimum Lease Receipt Table (Details) $ in Millions	Dec. 31, 2018 USD ($)
Accounting Policies [Abstract]
Operating Leases, Future Minimum Payments Receivable, Current	$ 342
Operating Leases, Future Minimum Payments Receivable, in Two Years	261
Operating Leases, Future Minimum Payments Receivable, in Three Years	257
Operating Leases, Future Minimum Payments Receivable, in Four Years	224
Operating Leases, Future Minimum Payments Receivable, in Five Years	141
Operating Leases, Future Minimum Payments Receivable, Thereafter	239
Operating Leases, Future Minimum Payments Receivable	$ 1,464