Stock-Based Compensation (Stock Option Activity) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total intrinsic value of stock options exercised	$ 34	$ 92	$ 92
Cash received from stock option exercises	32	53	57
Income tax benefit from the exercise of stock options	12	31	33
Total fair value of stock options vested	$ 16	$ 13	$ 10