Stockholders' Equity - Repurchase of Common Stock (Details) - USD ($)	1 Months Ended	2 Months Ended	3 Months Ended			6 Months Ended
	Jul. 31, 2017	Jun. 30, 2017	Jul. 31, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 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
Stock repurchase program, remaining authorization		$ 1,900,000,000		$ 1,900,000,000		$ 1,900,000,000
Number of shares repurchased				3,536,308	435,140	3,545,828	1,134,485
Value of shares repurchased				$ 155,300,000	$ 20,000,000	$ 165,000,000	$ 52,000,000
Accelerated Share Repurchase Agreement
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount								$ 150,000,000.0
Number of shares repurchased		2,235,677
Subsequent Event | Accelerated Share Repurchase Agreement
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, remaining authorization	$ 129,600,000		$ 129,600,000
Number of shares repurchased	679,278
Average price per share (in dollars per share)			$ 44.47