Stockholders' Equity - Stock Repurchases (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Total cost	$ 140	$ 61	$ 44
Total shares (in shares)	2,510,376	1,190,995	1,549,434
Average price per share (in dollars per share)	$ 55.64	$ 51.22	$ 34.46

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration