Borrowings and Contractual Commitments Short-Term Borrowings (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Short-term Debt [Line Items]
Other Short-term Borrowings	$ 5,634	$ 5,788
Federal Home Loan Bank Advances [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	4,000	4,000
Short-term Debt, Weighted Average Interest Rate	0.23%	0.21%
Master Notes [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	1,280	1,554
Short-term Debt, Weighted Average Interest Rate	0.15%	0.28%
Dealer Collateral [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	354	232
Short-term Debt, Weighted Average Interest Rate	0.13%	0.10%
Other Short Term Borrowings [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	$ 0	$ 2
Short-term Debt, Weighted Average Interest Rate	0.00%	2.70%