Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions |
Jun. 30, 2019 |
Dec. 31, 2018 |
---|---|---|
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items] | ||
Unrecognized tax benefits, excluding related interest expense and penalties(a) | $ 234 | $ 251 |
Portion that, if recognized, would reduce tax expense and effective tax rate | 170 | $ 164 |
Decrease in Unrecognized Tax Benefits is Reasonably Possible | 53 | |
Decrease in Unrecognized Tax Benefits That Would Impact Effective Tax Rate | $ 24 |