Preferred and Common Stock - Schedule of Share Activity (Details) - shares		1 Months Ended	12 Months Ended
	Aug. 31, 2016	Aug. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock retirement (in shares)	(25,000,000)	(76,000,000)
Common stock outstanding, ending balance (in shares)			483,270,717
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock, beginning balance (in shares)			0	0	81,051,103
Issued for stock-based compensation plans (in shares)			0	0	(5,219,660)
Treasury stock retirement (in shares)					(75,831,443)
Reverse stock split (in shares)					0
Conversion of convertible notes (in shares)				0
Treasury stock, ending balance (in shares)			0	0	0
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock outstanding, beginning balance (in shares)			481,416,537	438,519,780	1,310,160,141
Issued for stock-based compensation plans (in shares)			(1,854,180)	(3,654,051)	(5,302,128)
Treasury stock retirement (in shares)					0
Reverse stock split (in shares)					(876,942,489)
Conversion of convertible notes (in shares)				39,242,706
Common stock outstanding, ending balance (in shares)			483,270,717	481,416,537	438,519,780