Share-Based Payments - Data Related to All Total Shareholder Return Units (Details) - Total Shareholder Return Units (TSRUs) [Member] - USD ($) $ / shares in Units, $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Weighted-average grant-date fair value per stock option (in dollars per share) | $ 7.42 | $ 6.23 | $ 5.83 |
| Total compensation cost related to nonvested awards not yet recognized, pre-tax | $ 246 | $ 232 | $ 164 |
| Weighted-average period over which nonvested award cost is expected to be recognized (years) | 1 year 7 months | 1 year 8 months 12 days | 1 year 10 months 24 days |