INVESTMENTS - Fair Value of AFS Securities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt securities AFS
Less than 12 months	$ 42,125	$ 96,451
12 months or longer	4,523	41,434
Total	46,648	137,885
Gross unrealized losses
Less than 12 months	1,041	802
12 months or longer	180	311
Total	1,221	1,113
Mortgage-backed securities - U.S. agency-sponsored
Debt securities AFS
Less than 12 months	7,937	9,780
12 months or longer	858	1,877
Total	8,795	11,657
Gross unrealized losses
Less than 12 months	225	242
12 months or longer	52	38
Total	277	280
Mortgage-backed securities - Non-U.S. residential
Debt securities AFS
Less than 12 months	360	208
12 months or longer	0	1
Total	360	209
Gross unrealized losses
Less than 12 months	3	0
12 months or longer	0	0
Total	3	0
Commercial and other
Debt securities AFS
Less than 12 months	38	16
12 months or longer	8	27
Total	46	43
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	1	0
Total	1	0
Mortgage-backed securities
Debt securities AFS
Less than 12 months	8,335	10,004
12 months or longer	866	1,905
Total	9,201	11,909
Gross unrealized losses
Less than 12 months	228	242
12 months or longer	53	38
Total	281	280
U.S. Treasury
Debt securities AFS
Less than 12 months	3,062	45,484
12 months or longer	0	26,907
Total	3,062	72,391
Gross unrealized losses
Less than 12 months	2	248
12 months or longer	0	132
Total	2	380
Agency obligations
Debt securities AFS
Less than 12 months	0	781
12 months or longer	249	3,897
Total	249	4,678
Gross unrealized losses
Less than 12 months	0	2
12 months or longer	7	18
Total	7	20
U.S. Treasury and federal agency securities
Debt securities AFS
Less than 12 months	3,062	46,265
12 months or longer	249	30,804
Total	3,311	77,069
Gross unrealized losses
Less than 12 months	2	250
12 months or longer	7	150
Total	9	400
State and municipal securities
Debt securities AFS
Less than 12 months	968	362
12 months or longer	236	266
Total	1,204	628
Gross unrealized losses
Less than 12 months	415	62
12 months or longer	21	27
Total	436	89
Foreign government
Debt securities AFS
Less than 12 months	26,966	35,485
12 months or longer	2,963	8,170
Total	29,929	43,655
Gross unrealized losses
Less than 12 months	235	149
12 months or longer	84	92
Total	319	241
Corporate
Debt securities AFS
Less than 12 months	2,540	2,916
12 months or longer	61	123
Total	2,601	3,039
Gross unrealized losses
Less than 12 months	155	98
12 months or longer	7	3
Total	162	101
Asset-backed securities
Debt securities AFS
Less than 12 months	136	112
12 months or longer	148	166
Total	284	278
Gross unrealized losses
Less than 12 months	6	1
12 months or longer	8	1
Total	14	2
Other debt securities
Debt securities AFS
Less than 12 months	118	1,307
12 months or longer	0	0
Total	118	1,307
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	$ 0	$ 0