Stockholders' Equity - Common Stock Activity (Detail)	3 Months Ended
	Mar. 31, 2017 shares
Actual number of shares of common stock outstanding
Beginning of period	357,465,614
Shares of common stock issued through compensation plans	578,922
Employee benefit trust activity	187,530
Repurchases of common stock	(929,851)
End of period	357,302,215