Stock-Based Compensation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary of stock-based compensation expense
Pre-tax compensation expense	$ 30	$ 50	$ 51
Tax benefit	(10)	(18)	(16)
Total stock-based compensation recorded as expense, net of tax	$ 20	$ 32	$ 35