Stock-Based Compensation (Details 3) (USD $) In Millions, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Additional disclosures
Weighted average remaining vesting period	2 years	2 years
Stock Options
Shares
Outstanding at the beginning of the period (in shares)	24	30
Granted (in shares)		1
Exercised (in shares)	2	2
Forfeited (in shares)		1
Outstanding at the end of the period (in shares)	22	28
Option shares vested and expected to vest at the end of the period	22	28
Option shares exercisable at the end of the period	20	23
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 22	$ 21
Granted (in dollars per share)	$ 22	$ 20
Exercised (in dollars per share)	$ 16	$ 11
Forfeited (in dollars per share)	$ 22	$ 23
Outstanding at the end of the period (in dollars per share)	$ 22	$ 22
Option shares vested and expected to vest at the end of the period (in dollars per share)	$ 22	$ 22
Option shares exercisable at the end of the period (in dollars per share)	$ 23	$ 24
Aggregate intrinsic value
Exercised	$ 13	$ 21
Option shares vested and expected to vest at the end of the period	88	69
Option shares exercisable at the end of the period	69	37
Weighted average remaining option term
Outstanding at the end of the period	4 years	4 years
Option shares vested and expected to vest at the end of the period	4 years	4 years
Option shares exercisable at the end of the period	3 years	3 years
Additional disclosures
Total unrecognized compensation expense	$ 8	$ 12