Stock-Based Compensation (Stock Option Activity) (Details) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Number of Options (in shares):
Options outstanding at December 31, 2014 | shares	444,278
Exercised | shares	(178,017)
Forfeited or expired | shares	(3,979)
Options outstanding at September 30, 2015 | shares	262,282
Options exercisable at September 30, 2015 | shares	262,282
Weighted Average Exercise Price (in dollars per share):
Options outstanding at December 31, 2014	$ 43.56
Exercised	45.07
Forfeited or expired	44.72
Options outstanding at September 30, 2015	42.52
Options exercisable at September 30, 2015	$ 42.52
Aggregate Intrinsic Value - Options outstanding | $	$ 9
Aggregate Intrinsic Value - Options exercisable | $	$ 9