CONSOLIDATED BALANCE SHEET (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Receivables, allowances	$ 3	$ 3
Property and equipment, accumulated depreciation	$ 6,361	$ 6,324
Common shares, par value	$ 1.25	$ 1.25
Common shares, authorized	1,360,000,000	1,360,000,000
Common shares, issued	511,032,862	524,474,315
Common shares, outstanding	511,032,862	524,474,315
6.375 percent Mandatory Convertible Preference Shares, Series A
Preference shares, par value	$ 1.00	$ 1.00
Preference shares, liquidation	$ 50.00	$ 50.00
Preference shares, authorized	40,000,000	40,000,000
Preference shares, issued	13,799,711	13,800,000
Preference shares, outstanding	13,799,711	13,800,000