Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2020 |
Mar. 31, 2019 |
|
| Earnings Per Share Reconciliation [Abstract] | ||
| Net income | $ 600 | $ 796 |
| Participating share-based awards — allocated income | (5) | (5) |
| Net income available to common shareholders -- basic | 595 | 791 |
| Net income available to common shareholders -- diluted | $ 595 | $ 791 |
| Weighted average shares outstanding, basic (in shares) | 254.4 | 262.9 |
| Weighted average effects of dilutive securities - stock options and performance shares (in shares) | 1.5 | 1.9 |
| Weighted average shares outstanding, diluted (in shares) | 255.9 | 264.8 |
| Net income per common share, basic (in dollars per share) | $ 2.34 | $ 3.01 |
| Net income per common share, diluted (in dollars per share) | $ 2.33 | $ 2.99 |