Fair Value Accounting - Change in Level 3 Assets Unobservable Inputs (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Loans held for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 63.0		$ 3.0
Purchases and additions	90.0		154.0
Sales and payments	(71.0)		(80.0)
Transfers from Level 2 to Level 3	2.0		4.0
Change in fair value	0.0		3.0
Balance, end of period	84.0		84.0
Change in unrealized gains for the period	2.0		3.0
Servicing Contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	1,241.0	$ 1,178.0	1,127.0	$ 1,124.0
Purchases and additions	284.0	214.0	545.0	403.0
Sales and payments	(452.0)	(241.0)	(535.0)	(397.0)
Change in fair value	23.0	32.0	3.0	92.0
Realization of cash flows	(52.0)	(38.0)	(96.0)	(77.0)
Balance, end of period	1,044.0	1,145.0	1,044.0	1,145.0
Change in unrealized gains for the period	3.0	31.0	(6.0)	69.0
Interest rate lock commitments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	13.0	10.0	(2.0)	18.0
Purchases and additions	5,490.0	4,577.0	11,232.0	8,637.0
Settlement of IRLCs upon acquisition or origination of loans HFS	(5,481.0)	(4,580.0)	(11,213.0)	(8,647.0)
Change in fair value	2.0	1.0	7.0	0.0
Balance, end of period	24.0	8.0	24.0	8.0
Change in unrealized gains for the period	$ 24.0	$ 7.0	$ 24.0	$ 7.0

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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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- Definition

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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- Definition

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.

+ References

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- Definition

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

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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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- Definition

IRLC, settlements upon acquisition or origination of loans held for sale

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- Definition

Realization of cash flows

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