Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017	[1]
Statement Of Financial Position [Abstract]
Preferred stock, no par value	$ 0	$ 0
Preferred stock, authorized	1,000,000	1,000,000
Preferred stock, issued	0	0
Common stock, par value	$ 1	$ 1
Common stock, authorized	1,200,000,000	1,200,000,000
Common stock, issued	352,200,000	351,800,000
Treasury stock, shares	2,400,000	0

[1] The December 31, 2017 consolidated balance sheet has been derived from audited financial statements.