Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Income tax
Net UTB impacting the effective tax rate	$ 190		$ 190		$ 185
Period discussed over which the Company is not able to reasonably estimate the amount by which the liability for unrecognized tax benefits could change as a result of ongoing income tax authority examinations	12 months
Interest and penalties related to unrecognized tax benefits, expense (benefit) recognized on a gross basis	1	(1)	5	(5)
Interest and penalties related to unrecognized tax benefits, accrued on a gross basis	47		47		44
Deferred tax assets valuation allowance	$ 27		$ 27		$ 29
Reconciliation of Effective Income Tax Rate
Effective tax rate (as a percent)	27.40%	30.10%	28.20%	29.50%
Change in effective income tax rate from prior reporting period to current reporting period (as a percent)	(2.70%)		(1.30%)
Aggregative effective income tax rate change from factors which decreased rate from prior reporting period to current reporting period (as a percent)			(3.00%)
Aggregative effective income tax rate change from factors which increased rate from prior reporting period to current reporting period (as a percent)			1.70%