Collateralized Securities Transactions (Schedule Of Repurchase Agreements Accounted For As Secured Borrowings) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	$ 6,066,372	$ 7,534,443
Reverse Repurchase Agreements	6,014,438	7,500,002
Repurchase Agreements [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	6,066,372	7,534,443
Repurchase Agreements [Member] | Overnight and Continuous [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	3,947,295	5,145,495
Repurchase Agreements [Member] | Up to 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	1,718,976	2,288,545
Repurchase Agreements [Member] | 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements		100,403
Repurchase Agreements [Member] | Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	400,101
Repurchase Agreements [Member] | U.S. government agency MBS [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	4,996,698	6,664,321
Repurchase Agreements [Member] | U.S. government agency MBS [Member] | Overnight and Continuous [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	3,923,623	5,117,811
Repurchase Agreements [Member] | U.S. government agency MBS [Member] | Up to 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	672,974	1,546,510
Repurchase Agreements [Member] | U.S. government agency MBS [Member] | Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	400,101
Repurchase Agreements [Member] | MBS (Gestational Repo) [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	1,046,002	842,438
Repurchase Agreements [Member] | MBS (Gestational Repo) [Member] | Up to 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	1,046,002	742,035
Repurchase Agreements [Member] | MBS (Gestational Repo) [Member] | 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements		100,403
Repurchase Agreements [Member] | SBA loans [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	23,672	27,684
Repurchase Agreements [Member] | SBA loans [Member] | Overnight and Continuous [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase Agreements	23,672	27,684
Reverse Repurchase Agreements [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	6,014,438	7,500,002
Reverse Repurchase Agreements [Member] | Overnight and Continuous [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	828,399	1,231,027
Reverse Repurchase Agreements [Member] | Up to 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	4,873,952	3,272,880
Reverse Repurchase Agreements [Member] | 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	312,087	2,421,037
Reverse Repurchase Agreements [Member] | Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements		575,058
Reverse Repurchase Agreements [Member] | U.S. government agency MBS [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	4,965,382	6,650,352
Reverse Repurchase Agreements [Member] | U.S. government agency MBS [Member] | Overnight and Continuous [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	828,399	1,231,027
Reverse Repurchase Agreements [Member] | U.S. government agency MBS [Member] | Up to 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	3,824,896	2,525,188
Reverse Repurchase Agreements [Member] | U.S. government agency MBS [Member] | 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	312,087	2,319,079
Reverse Repurchase Agreements [Member] | U.S. government agency MBS [Member] | Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements		575,058
Reverse Repurchase Agreements [Member] | MBS (Gestational Repo) [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	1,049,056	849,650
Reverse Repurchase Agreements [Member] | MBS (Gestational Repo) [Member] | Up to 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements	$ 1,049,056	747,692
Reverse Repurchase Agreements [Member] | MBS (Gestational Repo) [Member] | 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Reverse Repurchase Agreements		$ 101,958