Short-Term Borrowings (Components of Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Abstract]
Securities sold under repurchase agreements	$ 679	$ 469
Derivative collateral	474	542
Other secured borrowings	39	0
Other short-term borrowings	$ 1,192	$ 1,011