Commitments and Contingencies (Schedule of Annual Rentals on a Net Lease Basis) (Details) $ in Millions |
Dec. 31, 2018
USD ($)
|
|---|---|
| Lease Commitments [Line Items] | |
| Operating Leases, Future Minimum Payments Due, Next Twelve Months | $ 215 |
| Operating Leases, Future Minimum Payments Due in Two Years | 181 |
| Operating Leases, Future Minimum Payments Due in Three Years | 157 |
| Operating Leases, Future Minimum Payments Due in Four Years | 121 |
| Operating Leases, Future Minimum Payments, Due in Five Years | 85 |
| Operating Leases, Future Minimum Payments Due Thereafter | $ 200 |