Outstanding and Weighted Average Common Shares - Changes in Outstanding Common Shares (Detail) - shares	12 Months Ended			46 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Earnings Per Share [Abstract]
Balance at January 1	286,000,000	285,800,000	325,300,000
Shares issued	28,750,000	0	0
Activity related to restricted stock awards, net	1,100,000	800,000	600,000
Stock options exercised	200,000	200,000	3,300,000
PSU vested	400,000	600,000	0
Shares repurchased	0	(1,450,000)	(43,350,000)	(64,110,000)
Balance at December 31	316,500,000	286,000,000	285,800,000	316,500,000