Stockholders' Equity - Shares Repurchased (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Number of shares repurchased (in shares)	5,600,000	7,700,000	2,300,000
Average price per share (in dollars per share)	$ 122.72	$ 117.02	$ 127.04
Total cost of repurchases	$ 683	$ 903	$ 294