Income Taxes - Changes in Total Gross Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Balance, beginning of year	$ 33	$ 33	$ 21
Tax positions related to current year:
Additions	7	4	6
Reductions	0	0	0
Tax positions related to prior years:
Additions	2	1	18
Reductions	(1)	(1)	(3)
Settlements	0	0	0
Statutes of limitation expirations	(4)	(4)	(9)
Balance, end of year	$ 37	$ 33	$ 33