Stockholders' Equity - Repurchase of Common Stock (Details) - USD ($)	1 Months Ended	3 Months Ended		4 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Aug. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	May 31, 2017	Mar. 31, 2017	Jul. 31, 2015	Aug. 31, 2007
July 2015 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount									$ 1,500,000,000
Stock repurchase program, number of shares authorized to be repurchased										20,000,000
Stock repurchase program, authorized increase								$ 1,500,000,000.0
Number of shares repurchased		1,661,782	3,545,828		5,198,090	4,680,313
Value of shares repurchased		$ 72,400,000	$ 165,000,000		$ 227,700,000	$ 217,000,000
Accelerated Share Repurchase Agreement
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount	$ 400,000,000	$ 400,000,000			400,000,000		$ 150,000,000.0
Number of shares repurchased	7,368,179			2,914,955
Value of shares repurchased					$ 320,000,000
Stock repurchase program, remaining authorization				$ 129,600,000
Average price per share (in dollars per share)				$ 44.47