Commitments and Contingencies (Future minimum lease payments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense, Minimum Rentals	$ 122	$ 129	$ 136
Real estate
Operating Leased Assets [Line Items]
2012	76
2013	64
2014	53
2015	42
2016	31
Thereafter	73
Total	339
Non-rental equipment
Operating Leased Assets [Line Items]
2012	37
2013	17
2014	12
2015	10
2016	6
Thereafter	10
Total	$ 92