Fair Value Measurements (Details 2) (Fair Value, Measurements, Recurring, USD $) In Millions, unless otherwise specified			9 Months Ended
	Sep. 30, 2012 Level 2 Financial Products	Dec. 31, 2011 Level 2 Financial Products	Sep. 30, 2012 Level 3 Guarantees	Sep. 30, 2011 Level 3 Guarantees
Roll-forward of liabilities measured at fair value using Level 3 inputs
Balance at beginning of year			$ 7	$ 10
Acquisitions			6
Issuance of guarantees			7	2
Expiration of guarantees			(3)	(5)
Balance at end of period			17	7
Fair Value, Impaired Loans
Impaired loans	$ 201	$ 141