Stockholders' Equity - Shares of Common Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance (in shares)	209,709,046	219,012,050	226,126,674
Incentive Plan and Awards (in shares)	1,512,035	1,688,931	1,310,778
Stock Options Exercised (in shares)	344,686	786,931	575,662
Treasury Stock Purchased (in shares)	(3,276,589)	(11,778,866)	(9,001,064)
Ending balance (in shares)	208,289,178	209,709,046	219,012,050