INVESTMENT SECURITIES - Schedule of Gross Unrealized Losses and Fair Values of Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Fair Value	$ 4,574	$ 3,999
Gross Unrealized Losses	(76)	(30)
Fair Value	4,447	2,308
Gross Unrealized Losses	(137)	(58)
Fair Value	9,021	6,307
Gross Unrealized Losses	(213)	(88)
U.S. Treasury and agency obligations \| U.S. Treasury and other U.S. government corporations and agencies
Investment [Line Items]
Fair Value	179	273
Gross Unrealized Losses	(1)	(1)
Fair Value	153	130
Gross Unrealized Losses	(2)	(1)
Fair Value	332	403
Gross Unrealized Losses	(3)	(2)
Mortgage-backed securities \| U.S. Treasury and other U.S. government corporations and agencies
Investment [Line Items]
Fair Value	956	581
Gross Unrealized Losses	(16)	(2)
Fair Value	1,019	672
Gross Unrealized Losses	(38)	(17)
Fair Value	1,975	1,253
Gross Unrealized Losses	(54)	(19)
Tax-exempt municipal securities
Investment [Line Items]
Fair Value	809	1,590
Gross Unrealized Losses	(9)	(16)
Fair Value	1,648	661
Gross Unrealized Losses	(28)	(12)
Fair Value	2,457	2,251
Gross Unrealized Losses	(37)	(28)
Residential Mortgage-backed securities
Investment [Line Items]
Fair Value	0	20
Gross Unrealized Losses	0	0
Fair Value	15	3
Gross Unrealized Losses	0	0
Fair Value	15	23
Gross Unrealized Losses	0	0
Commercial Mortgage-backed securities
Investment [Line Items]
Fair Value	372	131
Gross Unrealized Losses	(8)	(1)
Fair Value	133	28
Gross Unrealized Losses	(6)	(1)
Fair Value	505	159
Gross Unrealized Losses	(14)	(2)
Asset-backed securities
Investment [Line Items]
Fair Value	824	107
Gross Unrealized Losses	(7)	0
Fair Value	40	10
Gross Unrealized Losses	0	0
Fair Value	864	117
Gross Unrealized Losses	(7)	0
Corporate debt securities
Investment [Line Items]
Fair Value	1,434	1,297
Gross Unrealized Losses	(35)	(10)
Fair Value	1,439	804
Gross Unrealized Losses	(63)	(27)
Fair Value	2,873	2,101
Gross Unrealized Losses	$ (98)	$ (37)

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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), in continuous unrealized loss position for more than 12 months.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer.

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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), in unrealized loss position.

+ References

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-Section 50
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-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
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