INVESTMENTS - Fair Value of AFS Securities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt securities AFS
Less than 12 months	$ 114,730	$ 60,316
12 months or longer	7,979	4,760
Total	122,709	65,076
Gross unrealized losses
Less than 12 months	1,053	267
12 months or longer	261	208
Total	1,314	475
Mortgage-backed securities - U.S. government-sponsored agency guaranteed
Debt securities AFS
Less than 12 months	14,217	3,588
12 months or longer	343	298
Total	14,560	3,886
Gross unrealized losses
Less than 12 months	208	30
12 months or longer	21	22
Total	229	52
Mortgage-backed securities - Non-U.S. residential
Debt securities AFS
Less than 12 months	22	1
12 months or longer	0	0
Total	22	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		7
12 months or longer		4
Total		11
Gross unrealized losses
Less than 12 months		0
12 months or longer		0
Total		0
Mortgage-backed securities
Debt securities AFS
Less than 12 months	14,239	3,596
12 months or longer	343	302
Total	14,582	3,898
Gross unrealized losses
Less than 12 months	208	30
12 months or longer	21	22
Total	229	52
U.S. Treasury
Debt securities AFS
Less than 12 months	52,548	25,031
12 months or longer	0	0
Total	52,548	25,031
Gross unrealized losses
Less than 12 months	413	49
12 months or longer	0	0
Total	413	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	101	836
12 months or longer	1,107	893
Total	1,208	1,729
Gross unrealized losses
Less than 12 months	2	34
12 months or longer	110	123
Total	112
Foreign government
Debt securities AFS
Less than 12 months	43,680	29,344
12 months or longer	6,510	3,502
Total	50,190	32,846
Gross unrealized losses
Less than 12 months	363	61
12 months or longer	129	61
Total	492	122
Corporate
Debt securities AFS
Less than 12 months	1,896	1,083
12 months or longer	19	24
Total	1,915	1,107
Gross unrealized losses
Less than 12 months	67	90
12 months or longer	1	1
Total	68	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	2,263	182
12 months or longer	0	0
Total	2,263	182
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	$ 0	$ 0