Stock-Based Compensation Plans - Summary of Performance of Share Activity (Detail) - Performance Shares [Member] - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share pay-out at plan	28,520	29,678	42,908
Actual share pay-out in following year	37,076	25,228	46,340
Weighted average fair value per share on grant date	$ 70.60	$ 63.07	$ 35.98