Income Taxes (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Realization assessment period for which cumulative operating income considered	3 years
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at the beginning of the period		$ 22	$ 20
Decrease due to closing of IRS audit		(9)	0
Increase in unrecognized tax benefits as a result of position taken during the current period		6	2
Balance, end of period	19	19	22
Interest on income taxes expense	$ 4	$ 4