Stockholders' Equity - Narrative (Details) - USD ($) shares in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 08, 2018	Feb. 29, 2016	Oct. 31, 2013
Class of Stock [Line Items]
Amount of common stock repurchases authorized					$ 1,100,000,000.0	$ 1,000,000,000.0	$ 750,000,000.0
Stock repurchase authorized amount increase	$ 416,700,000
Remaining amount available for future purchases of shares under approved repurchase program.	$ 750,000,000	$ 1,100,000,000
Value of shares repurchased during period		$ 750,000,000	$ 361,194,000	$ 373,794,000
Common Stock
Class of Stock [Line Items]
Repurchases of common stock (in shares)		10.2	6.9	7.0
Value of shares repurchased during period		$ 750,000,000	$ 361,200,000	$ 373,800,000