Preferred and Common Stock - Schedule of Share Activity (Detail) - shares			1 Months Ended		12 Months Ended
	Oct. 05, 2016	Aug. 31, 2016	Aug. 31, 2016	Aug. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock, beginning balance (in shares)					0	81,051,103	87,150,169
Common stock outstanding, beginning balance (in shares)	1,300,000,000.0				438,519,780	1,310,160,141	1,216,663,661
Treasury stock retirement (in shares)		(25,000,000)	(76,000,000)	(76,000,000)
Treasury stock, ending balance (in shares)					0	0	81,051,103
Common stock outstanding, ending balance (in shares)	400,000,000				481,416,537	438,519,780	1,310,160,141
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issued for stock-based compensation plans (in shares)						5,219,660	6,099,066
Treasury stock retirement (in shares)						(75,831,443)
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issued for stock-based compensation plans (in shares)					3,654,051	5,302,128	6,099,066
Number of common stock shares issued in a part of acquisition (in shares)							87,397,414
Reverse stock split (in shares)						(876,942,489)
Conversion of convertible notes (in shares)					39,242,706