Leases - ROU Assets and Lease Liabilities (Details) - USD ($) $ in Millions |
12 Months Ended | |||
|---|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2019 |
Jan. 01, 2019 |
|
| Lessee, Lease, Description [Line Items] | ||||
| ROU assets | $ 200 | |||
| Lease liabilities | $ 41 | $ 204 | $ 200 | |
| Rental expense | $ 1,944 | $ 1,821 | ||
| Property, plant and equipment | ||||
| Lessee, Lease, Description [Line Items] | ||||
| ROU assets | 187 | |||
| Short-term debt | ||||
| Lessee, Lease, Description [Line Items] | ||||
| Lease liabilities | 52 | |||
| Long-term debt | ||||
| Lessee, Lease, Description [Line Items] | ||||
| Lease liabilities | $ 151 | |||