Schedule of Information Related to Stock Repurchase Programs (Detail) - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Additional dollars authorized for repurchase		$ 500,000,000	$ 1,700,000,000	$ 1,200,000,000		$ 1,200,000,000
Aggregate purchase price paid for shares purchased as part of publicly announced program		$ 414,002,000	356,413,000	346,890,000
Stock Repurchase Program
Class of Stock [Line Items]
Total number of shares purchased as part of publicly announced programs		8,795,403
Average price paid per share for shares purchased as part of publicly announced program		$ 115.23
Aggregate purchase price paid for shares purchased as part of publicly announced program		$ 1,013,484,000
Stock Repurchase Programs Twenty Fifteen
Class of Stock [Line Items]
Maximum number of dollars that may yet be purchased under the program					$ 175,828,000
Stock Repurchase Programs Twenty Sixteen
Class of Stock [Line Items]
Additional dollars authorized for repurchase				$ 400,000,000
Total number of shares purchased	[1]			2,983,320
Total number of shares cancelled				2,500
Average price paid per share for forfeited restricted shares				$ 0.01
Aggregate purchase price paid				$ 346,890,000
Maximum number of dollars that may yet be purchased under the program				$ 285,891,000
Stock Repurchase Programs Twenty Sixteen | Stock Repurchase Program
Class of Stock [Line Items]
Total number of shares purchased as part of publicly announced programs				2,512,592
Average price paid per share for shares purchased as part of publicly announced program				$ 115.39
Aggregate purchase price paid for shares purchased as part of publicly announced program				$ 289,937,000
Stock Repurchase Programs Twenty Seventeen
Class of Stock [Line Items]
Additional dollars authorized for repurchase			$ 400,000,000
Total number of shares purchased	[1]		3,266,121
Total number of shares cancelled			10,791
Average price paid per share for forfeited restricted shares			$ 0.01
Total number of shares purchased as part of publicly announced programs			2,960,843
Aggregate purchase price paid			$ 356,413,000
Aggregate purchase price paid for shares purchased as part of publicly announced program			322,200,000
Maximum number of dollars that may yet be purchased under the program			$ 363,660,000
Stock Repurchase Programs Twenty Seventeen | Stock Repurchase Program
Class of Stock [Line Items]
Total number of shares purchased as part of publicly announced programs			2,960,843
Average price paid per share for shares purchased as part of publicly announced program			$ 108.83
Aggregate purchase price paid for shares purchased as part of publicly announced program			$ 322,231,000
Stock Repurchase Programs Twenty Eighteen
Class of Stock [Line Items]
Additional dollars authorized for repurchase		$ 500,000,000
Total number of shares purchased	[1]	3,435,992
Total number of shares cancelled		11,224
Average price paid per share for forfeited restricted shares		$ 0.01
Total number of shares purchased as part of publicly announced programs		3,321,968
Aggregate purchase price paid		$ 414,002,000
Aggregate purchase price paid for shares purchased as part of publicly announced program		401,300,000
Maximum number of dollars that may yet be purchased under the program		$ 462,344,000
Stock Repurchase Programs Twenty Eighteen | Stock Repurchase Program
Class of Stock [Line Items]
Total number of shares purchased as part of publicly announced programs		3,321,968
Average price paid per share for shares purchased as part of publicly announced program		$ 120.81
Aggregate purchase price paid for shares purchased as part of publicly announced program		$ 401,316,000
Stock Repurchase Programs Twenty Sixteen to Twenty Eighteen
Class of Stock [Line Items]
Additional dollars authorized for repurchase		$ 1,300,000,000
Total number of shares purchased	[1]	9,685,433
Total number of shares cancelled		24,515
Average price paid per share for forfeited restricted shares		$ 0.01
Aggregate purchase price paid		$ 1,117,305,000

[1] Includes 11,224, 10,791 and 2,500 of restricted shares that were forfeited by former employees pursuant to the terms of our restricted stock purchase plan during 2018, 2017 and 2016, respectively.