Income Taxes (Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Rollforward of Unrecognized Tax Benefits | |||
| Balance at beginning of period | $ 1,594 | $ 1,851 | $ 1,804 |
| Increases based on tax positions related to the current period | 83 | 63 | 172 |
| Increases based on tax positions related to prior periods | 34 | 170 | 14 |
| Decreases based on tax positions related to prior periods | (404) | (312) | (134) |
| Decreases related to settlements with taxing authorities | (139) | (155) | 0 |
| Decreases related to lapse of statute of limitations | (88) | (23) | (5) |
| Balance at end of period | 1,080 | 1,594 | 1,851 |
| Net unrecognized tax benefits | 746 | 873 | 1,110 |
| Interest Expense (Benefit) Net of Federal and State Income Tax Benefits | |||
| Recognized in income statements | (40) | (3) | 28 |
| Accrued at end of period | $ 91 | $ 147 | $ 150 |