Stock-Based Incentive Compensation Plans (Total unrecognized compensation expense for all stock-based incentive compensation plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 55	$ 47	$ 44
Stock options [Member]
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 9	$ 8	$ 8
Weighted average period (in years)	1 year 4 months 24 days	1 year 4 months 24 days	1 year 4 months 24 days
Performance Shares [Member]
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 12	$ 12	$ 11
Weighted average period (in years)	1 year 2 months 12 days	1 year 4 months 24 days	1 year
Non-employee Stock Appreciation Rights [Member]
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 2	$ 2	$ 1
Weighted average period (in years)	3 years 2 months 12 days	3 years 7 months 6 days	3 years
Restricted Stock Units And Non-Vested Stock [Member]
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 32	$ 25	$ 24
Weighted average period (in years)	1 year 1 month 6 days	1 year 2 months 12 days	1 year