Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Statement of Financial Position [Abstract] | ||
| Allowance for doubtful accounts | $ 10 | $ 11 |
| Preferred stock: | ||
| Shares issued | 0 | 0 |
| Shares outstanding | 0 | 0 |
| Par value | $ 0.01 | |
| Shares authorized | 30,000,000 | |
| Common stock: | ||
| Shares issued | 734,000,000 | 734,000,000 |
| Par value | $ 0.01 | |
| Shares authorized | 1,000,000,000 | |
| Treasury stock | (267,000,000) | (248,000,000) |