Common and Preferred Stock - Changes in Outstanding Common Shares (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stockholders Equity Note [Abstract]
Balance at January 1	315,100,000	316,500,000	286,000,000
Shares issued	0	0	28,800,000
Activity related to restricted stock awards, net	800,000	800,000	1,100,000
Stock options exercised	600,000	200,000	200,000
PSU vested	100,000	200,000	400,000
Shares repurchased	(25,200,000)	(2,600,000)	0
Balance at December 31	291,400,000	315,100,000	316,500,000