Short-Term Borrowings (Summary Of Short-Term Borrowings) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member]
Short-term Debt [Line Items]
Average amount outstanding	$ 2,657	$ 37	$ 0
Weighted average rate	1.13%	0.59%	0.00%
Highest month-end balance	$ 3,750	$ 750	$ 0
Year-end balance	$ 3,600	$ 500	$ 0
Weighted average rate on outstandings at year-end	1.44%	0.75%	0.00%
Short-term Debt [Member]
Short-term Debt [Line Items]
Year-end balance	$ 4,976	$ 827	$ 347
Security Owned and Sold, Not yet Purchased Fair Value, Security Sold, Not yet Purchased	95	25	30
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Year-end balance	927	106	111
Security Repurchase Agreements [Member]
Short-term Debt [Line Items]
Year-end balance	$ 354	$ 196	$ 206