INVESTMENTS - Fair Value of AFS Securities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt securities AFS
Less than 12 months	$ 107,883	$ 60,316
12 months or longer	6,146	4,760
Total	114,029	65,076
Gross unrealized losses
Less than 12 months	1,192	267
12 months or longer	240	208
Total	1,432	475
Mortgage-backed securities - U.S. government-sponsored agency guaranteed
Debt securities AFS
Less than 12 months	17,053	3,588
12 months or longer	262	298
Total	17,315	3,886
Gross unrealized losses
Less than 12 months	227	30
12 months or longer	22	22
Total	249	52
Mortgage-backed securities - Non-U.S. residential
Debt securities AFS
Less than 12 months	15	1
12 months or longer	1	0
Total	16	1
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
Commercial
Debt securities AFS
Less than 12 months	1	7
12 months or longer	0	4
Total	1	11
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
Mortgage-backed securities
Debt securities AFS
Less than 12 months	17,069	3,596
12 months or longer	263	302
Total	17,332	3,898
Gross unrealized losses
Less than 12 months	227	30
12 months or longer	22	22
Total	249	52
U.S. Treasury
Debt securities AFS
Less than 12 months	40,386	25,031
12 months or longer	0	0
Total	40,386	25,031
Gross unrealized losses
Less than 12 months	455	49
12 months or longer	0	0
Total	455	49
Agency obligations
Debt securities AFS
Less than 12 months		50
12 months or longer		0
Total		50
Gross unrealized losses
Less than 12 months		0
12 months or longer		0
Total		0
U.S. Treasury and federal agency securities
Debt securities AFS
Less than 12 months		25,081
12 months or longer		0
Total		25,081
Gross unrealized losses
Less than 12 months		49
12 months or longer		0
Total		49
State and municipal
Debt securities AFS
Less than 12 months	191	836
12 months or longer	1,215	893
Total	1,406	1,729
Gross unrealized losses
Less than 12 months	5	34
12 months or longer	114	123
Total	119
Foreign government
Debt securities AFS
Less than 12 months	46,138	29,344
12 months or longer	4,629	3,502
Total	50,767	32,846
Gross unrealized losses
Less than 12 months	389	61
12 months or longer	102	61
Total	491	122
Corporate
Debt securities AFS
Less than 12 months	3,017	1,083
12 months or longer	39	24
Total	3,056	1,107
Gross unrealized losses
Less than 12 months	116	90
12 months or longer	2	1
Total	118	91
Asset-backed securities
Debt securities AFS
Less than 12 months	3	194
12 months or longer	0	39
Total	3	233
Gross unrealized losses
Less than 12 months	0	3
12 months or longer	0	1
Total	0	4
Other debt securities
Debt securities AFS
Less than 12 months	1,079	182
12 months or longer	0	0
Total	1,079	182
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	$ 0	$ 0