Short-Term Borrowings (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Short-term Debt [Abstract]
Number of maturity days of short-term borrowings, maximum	30
Secured Debt, Repurchase Agreements Overnight	$ 469
Example1 of term repurchase security agreement term	30
Term repurchase securitiy agreement term example2	60
Secured Debt, Repurchase Agreements Term	$ 46
Percentage of outstanding advance for unencumbered collateral	100.00%
Amount available for FHLB advances	$ 11,100
Amount available for federal reserve borrowings	$ 4,200