Postretirement Benefits (Details 6) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Employee savings plan
Employer match of employee contributions of up to the first 3% of eligible compensation (as a percent)	100.00%
Maximum threshold percentage of eligible employee compensation, matched 100% by employer	3.00%
Employer match of employee contributions of over 3% and up to 5% of eligible compensation (as a percent)	50.00%
Minimum threshold percentage of eligible employee compensation, matched 50% by employer	3.00%
Maximum threshold percentage of eligible employee compensation, matched 50% by employer (as a percent)	5.00%
Employer matching contribution to plan	$ 9	$ 9	$ 8
Class A common stock held by plan participants (in shares)	0.2	0.2