Consolidated Balance Sheet (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 1.00
Preferred stock, shares authorized	20,000,000
Preferred stock, shares issued	575,000
Preferred stock, liquidation preference per share	$ 1,000
Cumulative mandatory convertible series	8.00%
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	600,000,000	600,000,000
Common stock, shares issued	316,719,379	286,045,586