Share-Based Compensation - Schedule of Share and Dividend Equivalent Share Award Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Value of share equivalents
Market price of Company's stock	$ 81.35	$ 82.15
Phantom Stock and Performance Stock Units
Number of share equivalents
Balance at beginning of the period (in shares)	393,844,000	472,830,000
Granted (in shares)	151,908,000	111,119,000
Forfeited share equivalents (in shares)	(59,550,000)	(22,956,000)
Vested share equivalents (in shares)	(130,497,000)	(158,573,000)
Balance at end of the period (in shares)	355,705,000	402,420,000
Value of share equivalents
Balance at beginning of the period (in shares)	$ 30,523	$ 39,600
Granted (in shares)	12,358	9,128
Forfeited share equivalents (in shares)	4,844	1,886
Vested share equivalents (in shares)	10,871	13,212
Balance at end of the period (in shares)	$ 28,937	$ 33,059