Outstanding and Weighted Average Common Shares - Changes in Outstanding Common Shares (Detail) - shares	12 Months Ended			34 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Earnings Per Share [Abstract]
Balance at January 1	285,834,964	325,300,000	341,500,000
Activity related to restricted common stock awards, net	800,000	600,000	800,000
Stock options exercised	200,000	3,300,000	2,300,000
PSU vested	600,000	0	0
Shares repurchased	(1,450,000)	(43,350,000)	(19,310,000)	(64,110,000)
Balance at December 31	286,045,586	285,834,964	325,300,000	286,045,586