Stockholders' Equity (Summary of Share Repurchase Activity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stockholders' Equity [Abstract]
Number of shares acquired on the open market	1,372,084	1,144,379	3,130,621	2,871,204
Average price per share	$ 18.24	$ 17.39	$ 15.99	$ 17.39
Total cost of acquired shares	$ 25	$ 20	$ 50	$ 50

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- Definition

The cash outflow to reacquire common stock during the period.

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- Definition

Total cost of shares repurchased divided by the total number of shares repurchased.

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Number of shares that have been repurchased during the period and are being held in treasury.

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