Stock-Based Compensation (Stock Option Activity) (Details) - Jun. 30, 2015 - USD ($) $ / shares in Units, $ in Millions	Total
Number of Options (in shares):
Options outstanding at December 31, 2014	444,278
Exercised	(166,017)
Forfeited or expired	(3,979)
Options outstanding at June 30, 2015	274,282
Options exercisable at June 30, 2015	274,282
Weighted Average Exercise Price (in dollars per share):
Options outstanding at December 31, 2014	$ 43.56
Exercised	45.19
Forfeited or expired	44.72
Options outstanding at June 30, 2015	42.56
Options exercisable at June 30, 2015	$ 42.56
Aggregate Intrinsic Value - Options outstanding	$ 10
Aggregate Intrinsic Value - Options exercisable	$ 10