Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Rental expense for property and equipment under operating lease agreements
Gross rental expense	$ 164	$ 158	$ 156
Less: sublease revenue	(4)	(2)	(2)
Less: Rock-McGraw rent credit	(19)	(18)	(18)
Net rental expense	$ 141	$ 138	$ 136