SECURITIES - Amortized Cost and Fair Value of Securities, by Contractual Maturities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Securities [Line Items]
Available for sale, due in one year or less, amortized cost	$ 45
Available for sale, due after one year but within five years, amortized cost	194
Available for sale, due after five years but within ten years, amortized cost	103
Available for sale, due after ten years, amortized cost	64
Available for sale, with contractual maturities, amortized cost	406
Amortized Cost	3,162	$ 3,380
Available for sale, due in one year or less, fair value	46
Available for sale, due after one year but within five years, fair value	194
Available for sale, due after five years but within ten years, fair value	103
Available for sale, due after ten years, fair value	65
Available for sale, with contractual maturities, fair value	408
Total securities available for sale, fair value	3,208	3,463
Held to maturity, due in one year or less, amortized cost	21
Held to maturity, due after one year but within five years, amortized cost	22
Held to maturity, due after five years but within ten years, amortized cost	122
Held to maturity, due after ten years, amortized cost	889
Held to maturity, with contractual maturities, amortized cost	1,054
Amortized Cost	3,202	2,868
Held to maturity, due in one year or less, fair value	21
Held to maturity, due after one year but within five years, fair value	22
Held to maturity, due after five years but within ten years, fair value	125
Held to maturity, due after ten years, fair value	924
Held to maturity, with contractual maturities, fair value	1,092
Held to maturity, fair value	3,267	2,973
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	1,286
Amortized Cost	1,286	959
Available for sale, fair value	1,311
Total securities available for sale, fair value	1,311	994
Held to maturity, amortized cost	1,174
Amortized Cost	1,174	769
Held to maturity, fair value	1,193
Held to maturity, fair value	1,193	798
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	1,171
Amortized Cost	1,171	1,094
Available for sale, fair value	1,183
Total securities available for sale, fair value	1,183	1,124
Held to maturity, amortized cost	690
Amortized Cost	690	562
Held to maturity, fair value	695
Held to maturity, fair value	695	579
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Available-for-sale, amortized cost	299
Amortized Cost	299	361
Available for sale, fair value	306
Total securities available for sale, fair value	306	378
Held to maturity, amortized cost	284
Amortized Cost	284	307
Held to maturity, fair value	287
Held to maturity, fair value	$ 287	$ 317

Schedule Of Securities [Line Items]

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