Fair Value Measurements (Details 2) (USD $) In Millions, unless otherwise specified			9 Months Ended
	Sep. 30, 2013 Level 2 Financial Products Nonrecurring basis	Dec. 31, 2012 Level 2 Financial Products Nonrecurring basis	Sep. 30, 2013 Level 3 Guarantees Recurring basis	Sep. 30, 2012 Level 3 Guarantees Recurring basis
Roll-forward of liabilities measured at fair value using Level 3 inputs
Balance at beginning of year			$ 14	$ 7
Acquisitions				6
Issuance of guarantees			6	7
Expiration of guarantees			(5)	(3)
Balance at end of period			15	17
Fair value of impaired loans
Impaired loans	$ 109	$ 117