Fair Value Measurements (Details 2) (Fair Value, Measurements, Recurring, USD $) In Millions, unless otherwise specified			6 Months Ended
	Jun. 30, 2012 Level 2 Financial Products	Dec. 31, 2011 Level 2 Financial Products	Jun. 30, 2012 Level 3 Guarantees	Jun. 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			3	1
Expiration of guarantees			(1)	(4)
Balance at end of period			15	7
Fair Value, Impaired Loans
Impaired loans	$ 219	$ 141