Investment Securities (Summary Of Amount Of Gross Unrealized Losses For Debt Securities And Estimated Fair Value) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Investment Securities Gross Unrealized Losses Less Than 12 Months	$ 4	$ 40
Investment Securities Estimated Fair Value Less Than 12 Months	1,645	2,858
Investment Securities Gross Unrealized Losses 12 Months or More	94	297
Investment Securities Estimated Fair Value 12 Months or More	5,206	9,375
Investment Securities Gross Unrealized Losses Total	98	337
Investment Securities Estimated Fair Value Total	6,851	12,233
Available-for-sale Securities [Member]
Investment [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	39
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,389	2,772
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	93	287
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	5,152	8,937
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	97	326
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 6,541	$ 11,709