SECURITIES - Amortized Cost and Fair Value of Securities, by Contractual Maturities (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Schedule Of Securities [Line Items]
Available for sale, due in one year or less, amortized cost	$ 346
Available for sale, due after one year but within five years, amortized cost	120
Available for sale, due after five years but within ten years, amortized cost	71
Available for sale, due after ten years, amortized cost	80
Available for sale, with contractual maturities, amortized cost	617
Amortized Cost	3,203	$ 3,275
Available for sale, due in one year or less, fair value	346
Available for sale, due after one year but within five years, fair value	122
Available for sale, due after five years but within ten years, fair value	71
Available for sale, due after ten years, fair value	79
Available for sale, with contractual maturities, fair value	618
Total securities available for sale, fair value	3,301	3,289
Held to maturity, due in one year or less, amortized cost	123
Held to maturity, due after one year but within five years, amortized cost	54
Held to maturity, due after five years but within ten years, amortized cost	123
Held to maturity, due after ten years, amortized cost	966
Held to maturity, with contractual maturities, amortized cost	1,266
Amortized Cost	3,050	3,275
Held to maturity, due in one year or less, fair value	125
Held to maturity, due after one year but within five years, fair value	55
Held to maturity, due after five years but within ten years, fair value	126
Held to maturity, due after ten years, fair value	1,004
Securities held to maturity, with contractual maturities, fair value	1,310
Held-to-maturity, fair value, net	3,162	3,305
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	1,156
Amortized Cost	1,156	1,310
Available for sale, fair value	1,200
Total securities available for sale, fair value	1,200	1,314
Held-to-maturity, amortized cost	893
Amortized Cost	893	949
Held-to-maturity, fair value	928
Held-to-maturity, fair value, net	928	955
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	1,045
Amortized Cost	1,045	1,234
Available for sale, fair value	1,080
Total securities available for sale, fair value	1,080	1,240
Held-to-maturity, amortized cost	632
Amortized Cost	632	721
Held-to-maturity, fair value	653
Held-to-maturity, fair value, net	653	720
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	385
Amortized Cost	385	341
Available for sale, fair value	403
Total securities available for sale, fair value	403	345
Held-to-maturity, amortized cost	259
Amortized Cost	259	308
Held-to-maturity, fair value	271
Held-to-maturity, fair value, net	$ 271	$ 309

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