Stock-Based Compensation (Schedule of Non-qualified Stock Option Activity) (Details) (USD $) In Millions, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options, Outstanding	16,804,136	17,862,501
Options, Outstanding, Weighted Average Exercise Price	$ 17.37	$ 17.30
Options, Outstanding, Weighted Average Remaining Contractual Term	3 years 4 months 26 days	4 years
Options, Outstanding, Intrinsic Value	$ 75	$ 42
Options, Grants in Period, Gross	11,299
Options, Grants in Period, Weighted Average Exercise Price	$ 18.34
Options, Exercises in Period	1,047,364
Options, Exercises in Period, Weighted Average Exercise Price	$ 16.30
Options, Forfeitures in Period	0
Options, Forfeitures in Period, Weighted Average Exercise Price	$ 0.00
Options, Expirations in Period	22,300
Options, Expirations in Period, Weighted Average Exercise Price	$ 17.72
Options, Exercisable	9,910,449
Options, Exercisable, Weighted Average Exercise Price	$ 18.88
Options, Exercisable, Weighted Average Remaining Contractual Term	3 years 1 month 6 days
Options, Exercisable, Intrinsic Value	31
Options, Vested and Expected to Vest, Outstanding	16,675,607
Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$ 17.38
Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	3 years 4 months 26 days
Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 74