Stockholders' Deficit - Repurchase of Common Stock (Details) - USD ($)		3 Months Ended		9 Months Ended
	Jun. 13, 2014	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	May 02, 2018	Mar. 31, 2017	Jul. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)	3,932,244
Value of shares repurchased		$ 0	$ 121,500,000	$ 67,300,000	$ 523,300,000
Shares purchased, average price per share (in usd per share)	$ 33.06
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)			2,959,638	1,560,633	13,535,170
Value of shares repurchased			$ 121,500,000	$ 67,200,000	$ 603,100,000
Shares purchased, average price per share (in usd per share)				$ 43.09
Common Stock | July 2015 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)			2,959,638		12,315,534
Value of shares repurchased			$ 121,500,000		$ 523,100,000
Shares purchased, average price per share (in usd per share)			$ 41.04		$ 42.47