Stockholders’ Equity - Summary of Stock Repurchase Activity (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Equity [Abstract]
Shares Repurchased | shares	24,000,000
Average Price per Share (in usd per share) | $ / shares	$ 41.71
Value of Shares Repurchased	$ 1,011
Shares Repurchased, Remaining Amount Authorized
Beginning balance	1,651
Repurchase of shares of common stock	(1,011)
Ending balance	$ 6,640
Treasury shares retired | shares	0