Income Taxes - Reconciliation of Tax Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Loss Contingency [Roll Forward]
Gross tax contingencies, beginning	$ 294	[1]	$ 229	[1]	$ 213
Gross increases to tax positions in prior periods	78		91		22
Gross decreases to tax positions in prior periods	(18)		(47)		(3)
Gross increases to current period tax positions	54		26		4
Audit settlements paid	(1)		(4)		(1)
Lapse of statute of limitations	0		(1)		(6)
Gross tax contingencies, ending	$ 407	[1]	$ 294	[1]	$ 229	[1]

[1] As of December 31, 2013, we had $407 million of tax contingencies, of which $346 million, if fully recognized, would decrease our effective tax rate.