CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Statement of Financial Position [Abstract] | ||
| Accounts receivable, allowance for doubtful accounts | $ 898 | |
| Property and equipment, accumulated depreciation and amortization | $ 4,879 | 4,739 |
| Other intangible assets, accumulated amortization | $ 920 | $ 883 |
| Common stock, par value (in dollars per share) | $ 0.05 | $ 0.05 |
| Common stock, authorized shares (in shares) | 262,500,000 | 262,500,000 |
| Common stock, shares issued (in shares) | 150,391,400 | 149,384,952 |
| Common stock in treasury (in shares) | 48,402,616 | 48,413,169 |