Investment Securities - Schedule of Amortized Cost, Unrealized Gains/(Losses) and Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 8,471
Securities available for sale at fair value	8,494	$ 8,047
Securities pledged as collateral	7,500	6,400
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	304	10
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	303	10
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	603	613
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Securities available for sale at fair value	603	613
Government agency issued MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,324	3,722
Gross Unrealized Gains	58	92
Gross Unrealized Losses	(37)	(2)
Securities available for sale at fair value	4,345	3,812
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	229
Gross Unrealized Gains	0
Gross Unrealized Losses	(1)
Fair Value	228
Government agency issued CMO
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,234	2,380
Gross Unrealized Gains	14	29
Gross Unrealized Losses	(31)	(3)
Securities available for sale at fair value	2,217	2,406
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	75
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	75
Other U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	794	672
Gross Unrealized Gains	6	12
Gross Unrealized Losses	(12)	0
Securities available for sale at fair value	788	684
Corporate and other debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		40
Gross Unrealized Gains		1
Gross Unrealized Losses		(1)
Securities available for sale at fair value		40
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		10
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		10
States and municipalities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	516	445
Gross Unrealized Gains	10	15
Gross Unrealized Losses	(1)	0
Securities available for sale at fair value	525	460
Securities available-for-sale, excluding interest only strip:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,471	7,872
Gross Unrealized Gains	88	149
Gross Unrealized Losses	(81)	(6)
Securities available for sale at fair value	8,478	8,015
Interest- only strips- AFS
Debt Securities, Available-for-sale [Line Items]
Securities available for sale at fair value	$ 16	$ 32

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, before 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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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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

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Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

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