Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions |
Sep. 30, 2018 |
Dec. 31, 2017 |
---|---|---|
Statement of Financial Position [Abstract] | ||
Properties, accumulated depreciation | $ 12,276 | $ 11,909 |
Common stock, par or stated value per share (in dollars per share) | $ 1.00 | $ 1.00 |
Common stock, shares authorized (in shares) | 1,350,000,000 | 1,350,000,000 |
Common stock, shares outstanding, net of treasury shares (in shares) | 272,346,940 | 284,157,187 |