Fair Value of Assets and Liabilities - Summary Of Changes In Level 3 Assets And Liabilities Measured At Fair Value (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair value, asset (liability), unrealized gain (loss), OCI		$ 0
Level 3
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ (14,000,000)	(23,000,000)
Total net gains (losses) included in net income	(9,000,000)	0
Purchases	0	0
Sales	0	0
Settlements	2,000,000	2,000,000
Net transfers into (out of) Level 3	0	0
Ending balance	(21,000,000)	(21,000,000)
Net unrealized gains (losses) included in net income	(9,000,000)	0
Fair value, asset (liability), unrealized gain (loss), OCI	0
Trading securities \| Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		1,000,000
Total net gains (losses) included in net income		0
Purchases		0
Sales		0
Settlements		0
Net transfers into (out of) Level 3		0
Ending balance		1,000,000
Net unrealized gains (losses) included in net income		0
Interest- only strips- AFS \| Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	32,000,000	19,000,000
Total net gains (losses) included in net income	5,000,000	(1,000,000)
Purchases	0	5,000,000
Sales	(27,000,000)	(8,000,000)
Settlements	0	0
Net transfers into (out of) Level 3	12,000,000	8,000,000
Ending balance	22,000,000	23,000,000
Net unrealized gains (losses) included in net income	2,000,000	(1,000,000)
Loans held for sale \| Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	12,000,000	14,000,000
Total net gains (losses) included in net income	1,000,000	0
Purchases	0	0
Sales	0	0
Settlements	(1,000,000)	(1,000,000)
Net transfers into (out of) Level 3	0	0
Ending balance	12,000,000	13,000,000
Net unrealized gains (losses) included in net income	1,000,000	$ 0
Loans held for investment \| Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	16,000,000
Total net gains (losses) included in net income	0
Purchases	0
Sales	0
Settlements	(2,000,000)
Net transfers into (out of) Level 3	3,000,000
Ending balance	17,000,000
Net unrealized gains (losses) included in net income	$ 0

Amount of unrealized gain (loss) recognized in other comprehensive income (OCI) from asset (liability) measured at fair value on recurring basis using unobservable input (level 3) and still held.

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Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held.

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Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy.

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No definition available.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of unrealized gain (loss) recognized in income for derivative asset (liability) after deduction of derivative liability (asset), measured at fair value using unobservable input (level 3) and still held.

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Amount of gain (loss) recognized in income from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value on recurring basis using unobservable input (level 3).

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Amount of purchases of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sales of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlements of financial instrument classified as a derivative asset (liability) after deduction of derivative liability, measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into (out of) level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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