Outstanding and Weighted Average Common Shares - Changes in Outstanding Common Shares (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Beginning balance (in shares)	304,900	291,400	315,100
Conversion of preferred stock (in shares)	0	11,600	0
Activity related to restricted stock awards, net (in shares)	1,000	900	800
Stock options exercised (in shares)	261	700	600
PSUs vested (in shares)	800	300	100
Shares repurchased (in shares)	0	0	(25,200)
Ending balance (in shares)	307,000	304,900	291,400