Stock-Based Compensation (Schedule of Non-qualified Stock Option Activity) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options, Outstanding	13,927,858	14,114,289
Options, Outstanding, Weighted Average Exercise Price	$ 18.29	$ 18.25
Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 9 months 19 days	3 years 1 month 6 days
Options, Outstanding, Intrinsic Value	$ 48	$ 36
Options, Grants in Period, Gross	0
Options, Grants in Period, Weighted Average Exercise Price	$ 0.00
Options, Exercises in Period	184,931
Options, Exercises in Period, Weighted Average Exercise Price	$ 15.56
Options, Forfeitures in Period	0
Options, Forfeitures in Period, Weighted Average Exercise Price	$ 0.00
Options, Expirations in Period	1,500
Options, Expirations in Period, Weighted Average Exercise Price	$ 17.39
Options, Exercisable	13,012,308
Options, Exercisable, Weighted Average Exercise Price	$ 18.50
Options, Exercisable, Weighted Average Remaining Contractual Term	2 years 6 months 2 days
Options, Exercisable, Intrinsic Value	43
Options, Vested and Expected to Vest, Outstanding	13,871,693
Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$ 18.30
Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term	2 years 9 months 19 days
Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 48