Securities - Schedule of Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Amortized Cost	$ 3,275	$ 3,401
Gross Unrealized Gains	24	5
Gross Unrealized Losses	(10)	(65)
Fair Value	3,289	3,341
U.S. government agencies
Schedule of Investments [Line Items]
Amortized Cost	152	188
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(1)
Fair Value	151	187
U.S. government-sponsored entities
Schedule of Investments [Line Items]
Amortized Cost	225	317
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	(4)
Fair Value	226	313
Agency mortgage-backed securities
Schedule of Investments [Line Items]
Amortized Cost	1,310	1,465
Gross Unrealized Gains	7	0
Gross Unrealized Losses	(3)	(36)
Fair Value	1,314	1,429
Agency collateralized mortgage obligations
Schedule of Investments [Line Items]
Amortized Cost	1,234	1,179
Gross Unrealized Gains	10	5
Gross Unrealized Losses	(4)	(23)
Fair Value	1,240	1,161
Commercial mortgage-backed securities
Schedule of Investments [Line Items]
Amortized Cost	341	229
Gross Unrealized Gains	6	0
Gross Unrealized Losses	(2)	(1)
Fair Value	345	228
States of the U.S. and political subdivisions
Schedule of Investments [Line Items]
Amortized Cost	11	21
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	11	21
Other debt securities
Schedule of Investments [Line Items]
Amortized Cost	2	2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 2	$ 2

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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