Stockholder's Equity - Narrative (Details) - USD ($)	1 Months Ended			2 Months Ended	12 Months Ended
	Dec. 31, 2018	Jul. 31, 2018	Jul. 31, 2017	Feb. 14, 2019	Dec. 31, 2011	Feb. 13, 2019	Dec. 14, 2018	Dec. 31, 2017
Stockholders Equity [Line Items]
Preferred stock, par value (in usd per share)	$ 0.001							$ 0.001
Preferred stock, shares outstanding (in shares)	70,000							70,000
Class of warrant or right, exercise price of warrants or rights (in usd per share)					$ 7
Class of warrant or right, number of securities called by warrants or rights (in shares)	10,000,000
Number of shares issued in transaction (in shares)			11,000,000
Stock repurchase program authorized amount							$ 1,000,000,000
Shares repurchased and retired (in shares)	10,000,000
Aggregate value of shares repurchased and retired	$ 536,000,000
Shares repurchased, average price per share (in usd per share)	$ 53.46
Subsequent Event
Stockholders Equity [Line Items]
Stock repurchase program authorized amount						$ 1,500,000,000.0
Shares repurchased and retired (in shares)				8,000,000
Aggregate value of shares repurchased and retired				$ 464,000,000
Shares repurchased, average price per share (in usd per share)				$ 59.47
Convertible Preferred Stock
Stockholders Equity [Line Items]
Preferred stock, par value (in usd per share)	$ 0.001
Preferred stock, shares outstanding (in shares)	0
Proceeds from issuance of preferred stock					$ 75,000,000
Proceeds from issuance of preferred stock, net of issuance costs (in shares)					75,000
Temporary equity, liquidation preference (in usd per share)					$ 1,000
Class of warrant or right, exercise price of warrants or rights (in usd per share)					$ 7
Class of warrant or right, number of securities called by warrants or rights (in shares)	10,000,000
Preferred stock, liquidation preference, percentage					4.00%
Offered Directly By The Company
Stockholders Equity [Line Items]
Number of shares issued in transaction (in shares)			5,000,000
Sale of stock, price per share (in usd per share)			$ 60.50
Gross proceeds received			$ 290,000,000
Gross proceeds received net of fees and expenses		$ 349,000,000	$ 288,000,000
Offered In Connection With Forward Sale Agreements
Stockholders Equity [Line Items]
Number of shares issued in transaction (in shares)		6,000,000	6,000,000
Sale of stock, price per share (in usd per share)			$ 58.08
Offered In Connection With Forward Sale Agreements | Morgan Stanley & Co. LLC
Stockholders Equity [Line Items]
Number of shares issued in transaction (in shares)			3,000,000