Commitments and Contingencies (Leases) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Commitments and Contingencies Disclosure [Abstract] | |||
| Total rentals, net of sublease rentals | $ 680 | $ 574 | $ 587 |
| Future total rentals on noncancellable operating leases | 975 | ||
| 2019 | 275 | ||
| 2020 | 146 | ||
| 2021 | 122 | ||
| 2022 | 100 | ||
| 2023 | 78 | ||
| Thereafter | $ 254 | ||