INVESTMENT SECURITIES - Gross Unrealized Losses and Fair Values of Securities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value
Less than 12 months	$ 4,990	$ 1,057
12 months or more	2,547	576
Total	7,537	1,633
Gross Unrealized Losses
Less than 12 months	(94)	(4)
12 months or more	(67)	(2)
Total	(161)	(6)
U.S. Treasury and agency obligations
Fair Value
Less than 12 months	201	225
12 months or more	355	0
Total	556	225
Gross Unrealized Losses
Less than 12 months	(3)	(1)
12 months or more	(7)	0
Total	(10)	(1)
Mortgage-backed securities
Fair Value
Less than 12 months	2,082	199
12 months or more	556	0
Total	2,638	199
Gross Unrealized Losses
Less than 12 months	(49)	(1)
12 months or more	(20)	0
Total	(69)	(1)
Tax-exempt municipal securities
Fair Value
Less than 12 months	68	16
12 months or more	34	19
Total	102	35
Gross Unrealized Losses
Less than 12 months	(1)	0
12 months or more	(1)	0
Total	(2)	0
Residential
Fair Value
Less than 12 months	358	17
12 months or more	8	0
Total	366	17
Gross Unrealized Losses
Less than 12 months	(6)	0
12 months or more	0	0
Total	(6)	0
Commercial
Fair Value
Less than 12 months	295	193
12 months or more	400	43
Total	695	236
Gross Unrealized Losses
Less than 12 months	(4)	(1)
12 months or more	(7)	0
Total	(11)	(1)
Asset-backed securities
Fair Value
Less than 12 months	530	65
12 months or more	425	498
Total	955	563
Gross Unrealized Losses
Less than 12 months	(3)	0
12 months or more	(1)	(2)
Total	(4)	(2)
Corporate debt securities
Fair Value
Less than 12 months	1,456	342
12 months or more	769	16
Total	2,225	358
Gross Unrealized Losses
Less than 12 months	(28)	(1)
12 months or more	(31)	0
Total	$ (59)	$ (1)