Stockholders' Deficit - Repurchase of Common Stock (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	May 02, 2018	Mar. 31, 2017	Jul. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Value of shares repurchased	$ 49,600,000	$ 77,100,000	$ 67,300,000	$ 401,800,000
July 2015 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount							$ 1,500,000,000
Stock repurchase program, authorized increase					$ 1,000,000,000.0	$ 1,500,000,000
Number of shares repurchased (in shares)	1,154,047	1,780,578	1,560,633	10,575,532
Value of shares repurchased	$ 49,500,000	$ 77,100,000	$ 67,200,000	$ 481,600,000
Shares purchased, average price per share (in usd per share)	$ 42.98		$ 43.09
Common Stock | July 2015 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)		1,780,578		9,355,896
Value of shares repurchased		$ 77,100,000		$ 401,600,000
Shares purchased, average price per share (in usd per share)		$ 43.29		$ 42.93