Significant Accounting Policies - Factored Receivables (Details) - USD ($) $ in Billions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Significant Accounting Policies | ||
| Gross proceeds from factored receivables | $ 2.1 | $ 2.2 |
| Accounts receivable sold and derecognized that remain uncollected from customers | 0.5 | 0.9 |
| Net gains and losses associated with the transfer of receivables | ||