Stock-Based Compensation (Details 2) (USD $) In Millions, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Additional disclosures
Remaining weighted average vesting period	2 years	2 years
Long-term stock awards
Unvested stock award shares
Balance at the beginning of the period (in shares)	8	8
Granted (in shares)	1.0	2.0
Vested (in shares)	2	2
Balance at the end of the period (in shares)	7	8
Weighted average grant date fair value
Balance at the beginning of the period (in dollars per share)	$ 17	$ 16
Granted (in dollars per share)	$ 22	$ 20
Vested (in dollars per share)	$ 17	$ 16
Forfeited (in dollars per share)	$ 16	$ 18
Balance at the end of the period (in dollars per share)	$ 18	$ 17
Additional disclosures
Total unrecognized compensation expense	$ 81	$ 83
Remaining weighted average vesting period	4 years	4 years
Total market value (at the vesting date) of stock award shares	$ 45	$ 32