Short-Term Borrowings (Summary Of Short-Term Borrowings) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member]
Short-term Debt [Line Items]
Average amount outstanding	$ 3,149	$ 2,971	$ 2,657
Weighted average rate	2.50%	2.01%	1.13%
Highest month-end balance	$ 4,950	$ 5,400	$ 3,750
Year-end balance	$ 1,000	$ 4,500	$ 3,600
Weighted average rate on outstandings at year-end	1.73%	2.61%	1.44%
Short-term Debt [Member]
Short-term Debt [Line Items]
Year-end balance	$ 2,053	$ 5,653	$ 4,976
Security Owned and Sold, Not yet Purchased Fair Value, Security Sold, Not yet Purchased	66	85	95
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Year-end balance	472	541	927
Security Repurchase Agreements [Member]
Short-term Debt [Line Items]
Year-end balance	$ 515	$ 527	$ 354