Stockholders' Equity - Common Stock Activity (Detail) - shares	1 Months Ended											12 Months Ended
	Nov. 30, 2016	Oct. 31, 2016	Sep. 30, 2016	Aug. 31, 2016	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Apr. 30, 2016	Mar. 31, 2016	Feb. 28, 2016	Jan. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Actual number of shares of common stock outstanding
Beginning of period											362,338,369	362,338,369	372,757,598	378,635,464
Shares of common stock issued through business combinations													52,698	75,083
Shares of common stock issued through compensation plans												3,482,699	4,107,501	4,940,195
Shares held for stock compensation plans												(280,339)
Repurchases of common stock	(326,679)	(139,937)	(183,968)	(224,800)	(1,286,936)	(1,478,685)	(1,320,614)	(1,368,352)	(429,617)	(687,473)	(628,054)	(8,075,115)	(14,579,428)	(10,893,144)
End of period												357,465,614	362,338,369	372,757,598