Borrowings and Contractual Commitments Short-Term Borrowings (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Short-term Debt [Line Items]
Other Short-term Borrowings	$ 3,303	$ 8,983
Federal Home Loan Bank Advances [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	1,500	7,000
Short-term Debt, Weighted Average Interest Rate	0.34%	0.14%
Master Notes [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	1,512	1,710
Short-term Debt, Weighted Average Interest Rate	0.30%	0.40%
Dealer Collateral [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	282	265
Short-term Debt, Weighted Average Interest Rate	0.17%
Other Short Term Borrowings [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	$ 9	$ 8
Short-term Debt, Weighted Average Interest Rate	2.70%	2.70%