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
Net UTB impacting the effective tax rate	$ 269		$ 269		$ 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	7	(3)	12	(8)
Interest and penalties related to unrecognized tax benefits, accrued on a gross basis	53		53		44
Deferred tax assets valuation allowance	$ 29		$ 29		$ 29
Reconciliation of Effective Income Tax Rate
Effective tax rate (as a percent)	27.40%	28.20%	28.00%	29.00%
Change in effective income tax rate from prior reporting period to current reporting period (as a percent)	(0.80%)		(1.00%)
Aggregative effective income tax rate change from factors which decreased rate from prior reporting period to current reporting period (as a percent)	(3.30%)		(2.70%)
Aggregative effective income tax rate change from factors which increased rate from prior reporting period to current reporting period (as a percent)	2.50%		1.70%