SECURITIES - Amortized Cost and Fair Value of Securities, by Contractual Maturities (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule Of Securities [Line Items]
Available for sale, due in one year or less, amortized cost	$ 185
Available for sale, due after one year but within five years, amortized cost	70
Available for sale, due after five years but within ten years, amortized cost	127
Available for sale, due after ten years, amortized cost	84
Available for sale, with contractual maturities, amortized cost	466
Amortized Cost	3,110	$ 3,380
Available for sale, due in one year or less, fair value	186
Available for sale, due after one year but within five years, fair value	69
Available for sale, due after five years but within ten years, fair value	126
Available for sale, due after ten years, fair value	84
Available for sale, with contractual maturities, fair value	465
Total securities available for sale, fair value	3,166	3,463
Held to maturity, due in one year or less, amortized cost	100
Held to maturity, due after one year but within five years, amortized cost	21
Held to maturity, due after five years but within ten years, amortized cost	145
Held to maturity, due after ten years, amortized cost	931
Held to maturity, with contractual maturities, amortized cost	1,197
Amortized Cost	3,043	2,868
Held to maturity, due in one year or less, fair value	101
Held to maturity, due after one year but within five years, fair value	21
Held to maturity, due after five years but within ten years, fair value	147
Held to maturity, due after ten years, fair value	966
Held to maturity, with contractual maturities, fair value	1,235
Held to maturity, fair value, net	3,114	2,973
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	1,074
Amortized Cost	1,074	959
Available for sale, fair value	1,103
Total securities available for sale, fair value	1,103	994
Held to maturity, amortized cost	889
Amortized Cost	889	769
Held to maturity, fair value	909
Held to maturity, fair value, net	909	798
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	1,242
Amortized Cost	1,242	1,094
Available for sale, fair value	1,263
Total securities available for sale, fair value	1,263	1,124
Held to maturity, amortized cost	643
Amortized Cost	643	562
Held to maturity, fair value	655
Held to maturity, fair value, net	655	579
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	328
Amortized Cost	328	361
Available for sale, fair value	335
Total securities available for sale, fair value	335	378
Held to maturity, amortized cost	314
Amortized Cost	314	307
Held to maturity, fair value	315
Held to maturity, fair value, net	$ 315	$ 317

Schedule Of Securities [Line Items]

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