Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] | |||
| Unrecognized tax benefits, beginning of year | $ 514 | $ 462 | $ 412 |
| Gross increases to tax positions in prior periods | 6 | 0 | 16 |
| Gross decreases to tax positions in prior periods | (28) | 0 | (11) |
| Gross increases to current period tax positions | 45 | 64 | 39 |
| Gross increases due to current period business acquisitions | 624 | 0 | 10 |
| Gross decreases due to settlements with taxing authorities | (2) | (12) | (4) |
| Unrecognized tax benefits, end of year | $ 1,159 | $ 514 | $ 462 |