Leases (details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Leases disclosure
Rent expense	$ 191	$ 206	$ 211
Future minimum annual rental payments due for 2012	143
Future minimum annual rental payments due for 2013	114
Future minimum annual rental payments due for 2014	89
Future minimum annual rental payments due for 2015	77
Future minimum annual rental payments due for 2016	56
Future minimum annual rental payments due for 2017 and thereafter	41
Approximate aggregate future sublease rental income that will partially offset the lease commitments	$ 8