Income Taxes - Reconciliation of Tax Contingencies (Parenthetical) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Income Tax Disclosure [Abstract]
Tax contingencies	$ 407	[1]	$ 294	[1]	$ 229	[1]	$ 213

[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.