Investment Debt Securities (Available-for-sale Debt Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 27,013	$ 24,687
Gross Unrealized Gains in AOCI	159	186
Gross Unrealized (Losses) in AOCI	(205)	(219)
Net Carrying Amount and Fair Value	26,967	24,654
U.S. Government & other government related
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	3,031	2,736
Gross Unrealized Gains in AOCI	13	4
Gross Unrealized (Losses) in AOCI	(85)	(129)
Net Carrying Amount and Fair Value	2,959	2,611
State or local housing agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	5	5
Gross Unrealized Gains in AOCI	0	0
Gross Unrealized (Losses) in AOCI	0	0
Net Carrying Amount and Fair Value	5	5
ABS \| FFELP
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	1,438	1,510
Gross Unrealized Gains in AOCI	40	45
Gross Unrealized (Losses) in AOCI	(3)	(2)
Net Carrying Amount and Fair Value	1,475	1,553
GSE MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	22,125	20,360
Gross Unrealized Gains in AOCI	105	137
Gross Unrealized (Losses) in AOCI	(116)	(88)
Net Carrying Amount and Fair Value	22,114	20,409
Government guaranteed MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	414	76
Gross Unrealized Gains in AOCI	1	0
Gross Unrealized (Losses) in AOCI	(1)	0
Net Carrying Amount and Fair Value	$ 414	$ 76

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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 excluding accrued interest, after allowance for credit loss, 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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Amount excluding accrued interest, 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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