Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Effective income tax rate	32.60%	32.20%	33.80%	35.80%
Unrecognized tax benefits	$ 59		$ 59		$ 74
Accrued interest and penalties associated with uncertain tax positions	$ 16		$ 16		$ 14