Borrowings and Contractual Commitments Short-Term Borrowings (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Other Short-term Borrowings	$ 1,024	$ 5,634
Federal Home Loan Bank Advances [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	$ 0	$ 4,000
Short-term Debt, Weighted Average Interest Rate	0.00%	0.23%
Master Notes [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	$ 582	$ 1,280
Short-term Debt, Weighted Average Interest Rate	0.20%	0.15%
Dealer Collateral [Member]
Short-term Debt [Line Items]
Other Short-term Borrowings	$ 442	$ 354
Short-term Debt, Weighted Average Interest Rate	0.20%	0.13%