Stock-Based Compensation (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 26	$ 25	$ 72	$ 70
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	6	4	15	9
Granted (in shares)			0.8
Granted (in dollars per share)			$ 23.39
Unrecognized compensation expense	16		16
Unrecognized compensation expense, period for recognition			2 years 3 months
Restricted stock and unit awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	20	21	57	61
Granted (in shares)			0.7
Granted (in dollars per share)			$ 77.81
Unrecognized compensation expense	$ 88		$ 88
Unrecognized compensation expense, period for recognition			1 year 8 months