Debt Securities (Schedule Of Cost And Estimated Fair Value Of Securities Available For Sale And Securities Held To Maturity By Contractual Maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities held to maturity, amortized cost	$ 1,143	$ 1,361
Debt Securities held to maturity, estimated fair value	1,215	1,372
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	200
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value	202
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost	828
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value	873
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost	267
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value	299
Debt Securities, Available-for-sale, Allocated and Single Maturity Date, Maturity, after 10 Years, Amortized Cost	111
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value	118
Debt Securities, Available-for-sale, Amortized Cost	26,092	22,332
Debt securities available for sale	27,154	22,606
Residential Agency [Member]
Debt Securities held to maturity, amortized cost	554	736
Debt Securities held to maturity, estimated fair value	569	732
Debt Securities, Available-for-sale, Amortized Cost	18,455	15,336
Debt securities available for sale	19,076	15,516
Residential Non-Agency [Member]
Debt Securities, Available-for-sale, Amortized Cost	1	1
Debt securities available for sale	1	1
Commercial Agency [Member]
Debt Securities held to maturity, amortized cost	589	625
Debt Securities held to maturity, estimated fair value	646	640
Debt Securities, Available-for-sale, Amortized Cost	5,659	4,720
Debt securities available for sale	5,999	4,766
Commercial Non Agency [Member]
Debt Securities, Available-for-sale, Amortized Cost	571	639
Debt securities available for sale	$ 586	$ 647

Held To Maturity Amortized Cost Basis before transfer from available for sale

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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