SECURITIES - Amortized Cost and Fair Value of Securities Available for Sale (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,006	$ 3,275
Gross Unrealized Gains	96	24
Gross Unrealized Losses	(1)	(10)
Total securities available for sale, fair value	3,101	3,289
U.S. Treasury [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	300
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Total securities available for sale, fair value	300
US Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	161	152
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(1)
Total securities available for sale, fair value	160	151
U.S. Government-Sponsored Entities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	135	225
Gross Unrealized Gains	2	1
Gross Unrealized Losses	0	0
Total securities available for sale, fair value	137	226
Agency Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,057	1,310
Gross Unrealized Gains	39	7
Gross Unrealized Losses	0	(3)
Total securities available for sale, fair value	1,096	1,314
Agency Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	941	1,234
Gross Unrealized Gains	35	10
Gross Unrealized Losses	0	(4)
Total securities available for sale, fair value	976	1,240
Commercial Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	396	341
Gross Unrealized Gains	20	6
Gross Unrealized Losses	0	(2)
Total securities available for sale, fair value	416	345
States of the U.S. and Political Subdivisions (municipals) [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	14	11
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Total securities available for sale, fair value	14	11
Other Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2	2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Total securities available for sale, 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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-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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