SECURITIES - Amortized Cost and Fair Value of Securities, by Contractual Maturities (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Securities [Line Items]
Available for sale, due in one year or less, amortized cost	$ 78
Available for sale, due after one year but within five years, amortized cost	240
Available for sale, due after five years but within ten years, amortized cost	78
Available for sale, due after ten years, amortized cost	106
Available for sale, with contractual maturities, amortized cost	502
Amortized Cost	3,431	$ 3,401
Available for sale, due in one year or less, fair value	77
Available for sale, due after one year but within five years, fair value	238
Available for sale, due after five years but within ten years, fair value	78
Available for sale, due after ten years, fair value	106
Available for sale, with contractual maturities, fair value	499
Total securities available for sale, fair value	3,403	3,341
Held to maturity, due in one year or less, amortized cost	42
Held to maturity, due after one year but within five years, amortized cost	175
Held to maturity, due after five years but within ten years, amortized cost	111
Held to maturity, due after ten years, amortized cost	978
Held to maturity, with contractual maturities, amortized cost	1,306
Amortized Cost	3,171	3,254
Held to maturity, due in one year or less, fair value	41
Held to maturity, due after one year but within five years, fair value	173
Held to maturity, due after five years but within ten years, fair value	112
Held to maturity, due after ten years, fair value	970
Securities held to maturity, with contractual maturities, fair value	1,296
Held-to-maturity, fair value, net	3,139	3,155
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	1,396
Amortized Cost	1,396	1,465
Available for sale, fair value	1,378
Total securities available for sale, fair value	1,378	1,429
Held-to-maturity, amortized cost	997
Amortized Cost	997	1,036
Held-to-maturity, fair value	987
Held-to-maturity, fair value, net	987	1,010
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	1,305
Amortized Cost	1,305	1,179
Available for sale, fair value	1,298
Total securities available for sale, fair value	1,298	1,161
Held-to-maturity, amortized cost	764
Amortized Cost	764	794
Held-to-maturity, fair value	751
Held-to-maturity, fair value, net	751	771
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	228
Amortized Cost	228	229
Available for sale, fair value	228
Total securities available for sale, fair value	228	228
Held-to-maturity, amortized cost	104
Amortized Cost	104	126
Held-to-maturity, fair value	105
Held-to-maturity, fair value, net	$ 105	$ 126

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