Stock-Based Compensation (Details 4) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Other restricted stock unit information
Weighted-average grant date fair value of restricted stock units granted during the year, per share	$ 20.61	[1]	$ 23.31	$ 16.37
Total fair value of restricted stock units vested during the year ($'s in millions)	$ 22		$ 35	$ 29

[1] Performance-based shares are valued utilizing a Monte Carlo valuation method using measures of total shareholder return. All other shares are valued at the grant-date market price or the grant-date market price less dividends projected to be paid over the vesting period.