INVESTMENTS - Fair Value of AFS Securities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair value
Less than 12 months	$ 96,451	$ 69,236
12 months or longer	41,434	118,258
Total	137,885	187,494
Gross unrealized losses
Less than 12 months	802	752
12 months or longer	311	2,468
Total	1,113	3,220
Mortgage-backed securities - U.S. government-sponsored agency guaranteed
Fair value
Less than 12 months	9,780	11,160
12 months or longer	1,877	13,143
Total	11,657	24,303
Gross unrealized losses
Less than 12 months	242	286
12 months or longer	38	439
Total	280	725
Mortgage-backed securities - Non-U.S. residential
Fair value
Less than 12 months	208	284
12 months or longer	1	2
Total	209	286
Gross unrealized losses
Less than 12 months	0	2
12 months or longer	0	0
Total	0	2
Mortgage-backed securities - Commercial
Fair value
Less than 12 months	16	79
12 months or longer	27	82
Total	43	161
Gross unrealized losses
Less than 12 months	0	1
12 months or longer	0	1
Total	0	2
Mortgage-backed securities
Fair value
Less than 12 months	10,004	11,523
12 months or longer	1,905	13,227
Total	11,909	24,750
Gross unrealized losses
Less than 12 months	242	289
12 months or longer	38	440
Total	280	729
U.S. Treasury
Fair value
Less than 12 months	45,484	8,389
12 months or longer	26,907	77,883
Total	72,391	86,272
Gross unrealized losses
Less than 12 months	248	42
12 months or longer	132	1,297
Total	380	1,339
Agency obligations
Fair value
Less than 12 months	781	277
12 months or longer	3,897	8,660
Total	4,678	8,937
Gross unrealized losses
Less than 12 months	2	2
12 months or longer	18	130
Total	20	132
U.S. Treasury and federal agency securities
Fair value
Less than 12 months	46,265	8,666
12 months or longer	30,804	86,543
Total	77,069	95,209
Gross unrealized losses
Less than 12 months	250	44
12 months or longer	150	1,427
Total	400	1,471
State and municipal securities
Fair value
Less than 12 months	362	1,614
12 months or longer	266	1,303
Total	628	2,917
Gross unrealized losses
Less than 12 months	62	34
12 months or longer	27	228
Total	89	262
Foreign government
Fair value
Less than 12 months	35,485	40,655
12 months or longer	8,170	15,053
Total	43,655	55,708
Gross unrealized losses
Less than 12 months	149	265
12 months or longer	92	331
Total	241	596
Corporate
Fair value
Less than 12 months	2,916	4,547
12 months or longer	123	2,077
Total	3,039	6,624
Gross unrealized losses
Less than 12 months	98	115
12 months or longer	3	42
Total	101	157
Asset-backed securities
Fair value
Less than 12 months	112	441
12 months or longer	166	55
Total	278	496
Gross unrealized losses
Less than 12 months	1	4
12 months or longer	1	0
Total	2	4
Other debt securities
Fair value
Less than 12 months	1,307	1,790
12 months or longer	0	0
Total	1,307	1,790
Gross unrealized losses
Less than 12 months	0	1
12 months or longer	0	0
Total	$ 0	$ 1