CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Treasury Stock - Common [Member]
Purchase of shares for company benefit plans, shares	1,206,419	37,871	54,493
Release of shares from company benefit plans, shares	186,529	255,091	231,081
Preferred Stock, Exchanged for Shares of Common Stock [Member] | Preferred Stock [Member]
Conversion of Stock, Shares Converted	236,048	1,412,009	0
Preferred Stock, Exchanged for Shares of Common Stock [Member] | Additional Paid-in Capital [Member]
Stock Issued During Period, Shares, Conversion of Convertible Securities	9,965,835	1,021,506	0
Contingent Convertible Senior Notes Exchanged for Shares of Common Stock [Member] | Additional Paid-in Capital [Member]
Stock Issued During Period, Shares, Conversion of Convertible Securities	0	55,427,782	0
Senior Notes Exchanged for Shares of Common Stock [Member] | Additional Paid-in Capital [Member]
Stock Issued During Period, Shares, Conversion of Convertible Securities	0	53,923,925	0