Stockholders' Equity - Shares of Common Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance (in shares)	226,126,674	228,605,485	229,293,783
Incentive Plan and Awards (in shares)	1,310,778	1,320,129	1,209,124
Stock Options Exercised (in shares)	575,662	1,997,362	4,156,728
Treasury Stock Purchased (in shares)	(9,001,064)	(5,796,302)	(6,054,150)
Ending balance (in shares)	219,012,050	226,126,674	228,605,485