SECURITIES - Amortized Cost and Fair Value of Securities, by Contractual Maturities (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Schedule Of Securities [Line Items]
Available for sale, due in one year or less, amortized cost	$ 343
Available for sale, due after one year but within five years, amortized cost	107
Available for sale, due after five years but within ten years, amortized cost	69
Available for sale, due after ten years, amortized cost	93
Available for sale, with contractual maturities, amortized cost	612
Amortized Cost	3,006	$ 3,275
Available for sale, due in one year or less, fair value	343
Available for sale, due after one year but within five years, fair value	108
Available for sale, due after five years but within ten years, fair value	69
Available for sale, due after ten years, fair value	93
Available for sale, with contractual maturities, fair value	613
Total securities available for sale, fair value	3,101	3,289
Held to maturity, due in one year or less, amortized cost	142
Held to maturity, due after one year but within five years, amortized cost	41
Held to maturity, due after five years but within ten years, amortized cost	144
Held to maturity, due after ten years, amortized cost	979
Held to maturity, with contractual maturities, amortized cost	1,306
Amortized Cost	2,966	3,275
Held to maturity, due in one year or less, fair value	143
Held to maturity, due after one year but within five years, fair value	41
Held to maturity, due after five years but within ten years, fair value	148
Held to maturity, due after ten years, fair value	1,017
Securities held to maturity, with contractual maturities, fair value	1,349
Held-to-maturity, fair value, net	3,072	3,305
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	1,057
Amortized Cost	1,057	1,310
Available for sale, fair value	1,096
Total securities available for sale, fair value	1,096	1,314
Held-to-maturity, amortized cost	811
Amortized Cost	811	949
Held-to-maturity, fair value	843
Held-to-maturity, fair value, net	843	955
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	941
Amortized Cost	941	1,234
Available for sale, fair value	976
Total securities available for sale, fair value	976	1,240
Held-to-maturity, amortized cost	571
Amortized Cost	571	721
Held-to-maturity, fair value	590
Held-to-maturity, fair value, net	590	720
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	396
Amortized Cost	396	341
Available for sale, fair value	416
Total securities available for sale, fair value	416	345
Held-to-maturity, amortized cost	278
Amortized Cost	278	308
Held-to-maturity, fair value	290
Held-to-maturity, fair value, net	$ 290	$ 309

Schedule Of Securities [Line Items]

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