Stockholders' Equity - Common Stock Activity (Detail)	6 Months Ended
	Jun. 30, 2017 shares
Actual number of shares of common stock outstanding
Beginning of period	357,465,614
Shares of common stock issued through compensation plans	852,068
Employee benefit trust activity	209,792
Repurchases of common stock	(1,950,063)
End of period	356,577,411