Stock-Based Compensation - Stock Option Activity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Stock option activity
Outstanding, Beginning Balance, Number of Shares Underlying Options	1.1
Granted, Number of Shares Underlying Options	0
Exercised, Number of Shares Underlying Options	0
Forfeited, Number of Shares Underlying Options	0
Outstanding, Ending Balance, Number of Shares Underlying Options	1.1
Options Exercisable, Number of Shares Underlying Options	0.9
Outstanding, Beginning Balance, Weighted Average Exercise Price per Share	$ 36.31
Granted, Weighted Average Exercise Price per Share	$ 0
Exercised, Weighted Average Exercise Price per Share	$ 0
Forfeited, Weighted Average Exercise Price per Share	$ 0
Outstanding, Ending Balance, Weighted Average Exercise Price per Share	$ 36.77
Options Exercisable, Weighted Average Exercise Price per Share	$ 35.86
Granted, Weighted Average Grant Date Fair Value per Share	$ 0
Outstanding, Beginning Balance, Weighted Average Remaining Contractual Life (In years)	4.0
Exercisable, Weighted Average Remaining Contractual Life (In years)	3.4
Outstanding, Ending Balance, Aggregate Intrinsic Value	$ 2	$ 7
Exercisable, Aggregate Intrinsic Value	$ 2
Outstanding, Ending Balance, Weighted Average Remaining Contractual Life (In years)	3.6