INVESTMENTS - Fair Value of AFS Securities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair value
Less than 12 months	$ 62,694	$ 96,451
12 months or longer	3,891	41,434
Total	66,585	137,885
Gross unrealized losses
Less than 12 months	280	802
12 months or longer	85	311
Total	365	1,113
Mortgage-backed securities - U.S. government-sponsored agency guaranteed
Fair value
Less than 12 months	3,588	9,780
12 months or longer	298	1,877
Total	3,886	11,657
Gross unrealized losses
Less than 12 months	30	242
12 months or longer	22	38
Total	52	280
Mortgage-backed securities - Non-U.S. residential
Fair value
Less than 12 months	1	208
12 months or longer	0	1
Total	1	209
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
Mortgage-backed securities - Commercial
Fair value
Less than 12 months	7	16
12 months or longer	4	27
Total	11	43
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
Mortgage-backed securities
Fair value
Less than 12 months	3,596	10,004
12 months or longer	302	1,905
Total	3,898	11,909
Gross unrealized losses
Less than 12 months	30	242
12 months or longer	22	38
Total	52	280
U.S. Treasury
Fair value
Less than 12 months	25,031	45,484
12 months or longer	0	26,907
Total	25,031	72,391
Gross unrealized losses
Less than 12 months	49	248
12 months or longer	0	132
Total	49	380
Agency obligations
Fair value
Less than 12 months	50	781
12 months or longer	0	3,897
Total	50	4,678
Gross unrealized losses
Less than 12 months	0	2
12 months or longer	0	18
Total	0	20
U.S. Treasury and federal agency securities
Fair value
Less than 12 months	25,081	46,265
12 months or longer	0	30,804
Total	25,081	77,069
Gross unrealized losses
Less than 12 months	49	250
12 months or longer	0	150
Total	49	400
State and municipal
Fair value
Less than 12 months	3,214	362
12 months or longer	24	266
Total	3,238	628
Gross unrealized losses
Less than 12 months	47	62
12 months or longer	0	27
Total	47	89
Foreign government
Fair value
Less than 12 months	29,344	35,485
12 months or longer	3,502	8,170
Total	32,846	43,655
Gross unrealized losses
Less than 12 months	61	149
12 months or longer	61	92
Total	122	241
Corporate
Fair value
Less than 12 months	1,083	2,916
12 months or longer	24	123
Total	1,107	3,039
Gross unrealized losses
Less than 12 months	90	98
12 months or longer	1	3
Total	91	101
Asset-backed securities
Fair value
Less than 12 months	194	112
12 months or longer	39	166
Total	233	278
Gross unrealized losses
Less than 12 months	3	1
12 months or longer	1	1
Total	4	2
Other debt securities
Fair value
Less than 12 months	182	1,307
12 months or longer	0	0
Total	182	1,307
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	$ 0	$ 0