Condensed Balance Sheets Parenthetical - USD ($) shares in Millions, $ in Millions |
Jun. 30, 2017 |
Dec. 31, 2016 |
Jun. 30, 2016 |
|---|---|---|---|
| ASSETS | |||
| Accumulated depreciation | $ 2,117.6 | $ 1,891.6 | $ 1,681.2 |
| Shareholders' equity: | |||
| Common stock, par value | $ 1.00 | $ 1.00 | $ 1.00 |
| Common stock, authorized (in shares) | 240.0 | 240.0 | 240.0 |
| Common stock, issued | 166.3 | 165.4 | 165.2 |
| Common stock, outstanding | 166.3 | 165.4 | 165.2 |