Investment Securities - Schedule of Amortized Cost, Unrealized Gains/(Losses) and Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 8,322
Securities available for sale at fair value	8,351	$ 8,047
Securities pledged as collateral	7,000	6,400
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	610	613
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Securities available for sale at fair value	610	613
Government agency issued MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,009	3,722
Gross Unrealized Gains	68	92
Gross Unrealized Losses	(39)	(2)
Securities available for sale at fair value	4,038	3,812
Government agency issued CMO
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,463	2,380
Gross Unrealized Gains	19	29
Gross Unrealized Losses	(41)	(3)
Securities available for sale at fair value	2,441	2,406
Other U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	733	672
Gross Unrealized Gains	5	12
Gross Unrealized Losses	(13)	0
Securities available for sale at fair value	725	684
Corporate and other debt
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40	40
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	(1)
Securities available for sale at fair value	40	40
States and municipalities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	467	445
Gross Unrealized Gains	9	15
Gross Unrealized Losses	(1)	0
Securities available for sale at fair value	475	460
Securities available-for-sale, excluding interest only strip:
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,322	7,872
Gross Unrealized Gains	101	149
Gross Unrealized Losses	(94)	(6)
Securities available for sale at fair value	8,329	8,015
Interest- only strips- AFS
Debt Securities, Available-for-sale [Line Items]
Securities available for sale at fair value	$ 22	$ 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 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 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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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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