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, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 44	$ 41	$ 39
Stock options [Member]
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 8	$ 8	$ 9
Weighted average period (in years)	1 year 4 months 24 days	1 year 6 months	1 year 10 months 24 days
Performance Shares [Member]
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 11	$ 9	$ 9
Weighted average period (in years)	1 year	1 year 6 months	1 year 6 months
Non-employee Stock Appreciation Rights [Member]
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 1	$ 3	$ 3
Weighted average period (in years)	3 years	3 years 2 months 12 days	3 years 4 months 24 days
Restricted Stock Units And Non-Vested Stock [Member]
Employee service share-based compensation, aggregate disclosures [Abstract]
Unrecognized stock-based incentive compensation expense	$ 24	$ 21	$ 18
Weighted average period (in years)	1 year	1 year	1 year 2 months 12 days