Debt Securities (Schedule Of Gross Unrealized Losses And Estimated Fair Value Of Securities Available For Sale) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Unrealized Loss And Fair Value On Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Estimated Fair Value		$ 82
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Estimated Fair Value		628
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(10)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Estimated Fair Value		710
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss		(10)
Available For Sale Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Estimated Fair Value	$ 1,733	3,870
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(10)	(42)
Available For Sale Securities, Continuous Unrealized Loss Position, Twelve Months or More, Estimated Fair Value	101	2,610
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	(28)
Available For Sale Securities, Continuous Unrealized Loss, Estimated Fair Value	1,834	6,480
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(10)	(70)
Residential Agency [Member]
Unrealized Loss And Fair Value On Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Estimated Fair Value		82
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Estimated Fair Value		501
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(5)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Estimated Fair Value		583
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss		(5)
Available For Sale Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Estimated Fair Value	914	2,402
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4)	(11)
Available For Sale Securities, Continuous Unrealized Loss Position, Twelve Months or More, Estimated Fair Value	101	2,505
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	(27)
Available For Sale Securities, Continuous Unrealized Loss, Estimated Fair Value	1,015	4,907
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(4)	(38)
Commercial Agency [Member]
Unrealized Loss And Fair Value On Securities [Line Items]
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Estimated Fair Value		0
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Estimated Fair Value		127
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(5)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Estimated Fair Value		127
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss		(5)
Available For Sale Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Estimated Fair Value	819	1,449
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(6)	(31)
Available For Sale Securities, Continuous Unrealized Loss Position, Twelve Months or More, Estimated Fair Value	0	73
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available For Sale Securities, Continuous Unrealized Loss, Estimated Fair Value	819	1,522
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (6)	(31)
Corporate and other debt securities [Member]
Unrealized Loss And Fair Value On Securities [Line Items]
Available For Sale Securities, Continuous Unrealized Loss Position, Less Than Twelve Months, Estimated Fair Value		19
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0
Available For Sale Securities, Continuous Unrealized Loss Position, Twelve Months or More, Estimated Fair Value		32
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		(1)
Available For Sale Securities, Continuous Unrealized Loss, Estimated Fair Value		51
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ (1)

Unrealized Loss And Fair Value Available For Sale Securities [Line Items]

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

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