Income taxes (Reconciliation of Total Gross Amounts of UTBs) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
|
| Reconciliation of total gross amounts of unrecognized tax benefits (excluding interest, penalties, foreign tax credits and the federal tax benefit of state taxes related to unrecognized tax benefits) | |||
| Beginning balance | $ 3,061 | $ 2,953 | $ 2,543 |
| Additions based on tax positions related to the current year | 215 | 173 | 447 |
| Additions based on tax positions related to prior years | 22 | 13 | 1 |
| Reductions for tax positions of prior years | (11) | (17) | (5) |
| Reductions for expiration of statute of limitations | 0 | 0 | (5) |
| Settlements | 0 | (61) | (28) |
| Ending balance | $ 3,287 | $ 3,061 | $ 2,953 |