Leases (details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Leases disclosure
Rent expense	$ 192	$ 191	$ 206
Future minimum annual rental payments due for 2013	164
Future minimum annual rental payments due for 2014	141
Future minimum annual rental payments due for 2015	118
Future minimum annual rental payments due for 2016	95
Future minimum annual rental payments due for 2017	59
Future minimum annual rental payments due for 2018 and thereafter	89
Approximate aggregate future sublease rental income that will partially offset the lease commitments	$ 6