Stockholders' Equity - Repurchase of Common Stock (Details) - USD ($)	1 Months Ended	3 Months Ended
	Feb. 28, 2018	Mar. 31, 2018	Mar. 31, 2017	May 08, 2018	Dec. 31, 2017	Nov. 30, 2017	Jul. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Value of shares repurchased		$ 324,700,000
Shares acquired under program (in shares)		69,963,816			61,485,423
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			$ 1,500,000,000.0
Number of shares repurchased (in shares)		8,794,954	0
Value of shares repurchased		$ 404,700,000
Accelerated Share Repurchase Agreement
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount						$ 400,000,000
Shares acquired under program (in shares)	8,308,692				7,089,056
Shares acquired, average price per share (in usd per share)	$ 48.14
Share Trading Plan | Common Stock Repurchase Set One
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)		7,575,318
Value of shares repurchased		$ 324,700,000
Shares acquired, average price per share (in usd per share)		$ 42.86
Subsequent Event | July 2015 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized increase				$ 1,000,000,000.0