INVESTMENTS - Fair Value of AFS Securities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Debt securities AFS
Less than 12 months	$ 59,108	$ 69,236
12 months or longer	76,078	118,258
Total	135,186	187,494
Gross unrealized losses
Less than 12 months	1,015	752
12 months or longer	756	2,468
Total	1,771	3,220
Mortgage-backed securities - U.S. agency-sponsored
Debt securities AFS
Less than 12 months	8,595	11,160
12 months or longer	5,718	13,143
Total	14,313	24,303
Gross unrealized losses
Less than 12 months	255	286
12 months or longer	90	439
Total	345	725
Mortgage-backed securities - Non-U.S. residential
Debt securities AFS
Less than 12 months	175	284
12 months or longer	1	2
Total	176	286
Gross unrealized losses
Less than 12 months	1	2
12 months or longer	0	0
Total	1	2
Commercial and other
Debt securities AFS
Less than 12 months	7	79
12 months or longer	61	82
Total	68	161
Gross unrealized losses
Less than 12 months	0	1
12 months or longer	0	1
Total	0	2
Mortgage-backed securities
Debt securities AFS
Less than 12 months	8,777	11,523
12 months or longer	5,780	13,227
Total	14,557	24,750
Gross unrealized losses
Less than 12 months	256	289
12 months or longer	90	440
Total	346	729
U.S. Treasury
Debt securities AFS
Less than 12 months	19,187	8,389
12 months or longer	54,921	77,883
Total	74,108	86,272
Gross unrealized losses
Less than 12 months	135	42
12 months or longer	448	1,297
Total	583	1,339
Agency obligations
Debt securities AFS
Less than 12 months	316	277
12 months or longer	6,857	8,660
Total	7,173	8,937
Gross unrealized losses
Less than 12 months	2	2
12 months or longer	46	130
Total	48	132
U.S. Treasury and federal agency securities
Debt securities AFS
Less than 12 months	19,503	8,666
12 months or longer	61,778	86,543
Total	81,281	95,209
Gross unrealized losses
Less than 12 months	137	44
12 months or longer	494	1,427
Total	631	1,471
State and municipal securities
Debt securities AFS
Less than 12 months	925	1,614
12 months or longer	960	1,303
Total	1,885	2,917
Gross unrealized losses
Less than 12 months	156	34
12 months or longer	41	228
Total	197	262
Foreign government
Debt securities AFS
Less than 12 months	25,294	40,655
12 months or longer	7,038	15,053
Total	32,332	55,708
Gross unrealized losses
Less than 12 months	337	265
12 months or longer	126	331
Total	463	596
Corporate
Debt securities AFS
Less than 12 months	2,598	4,547
12 months or longer	493	2,077
Total	3,091	6,624
Gross unrealized losses
Less than 12 months	126	115
12 months or longer	5	42
Total	131	157
Asset-backed securities
Debt securities AFS
Less than 12 months	476	441
12 months or longer	29	55
Total	505	496
Gross unrealized losses
Less than 12 months	2	4
12 months or longer	0	0
Total	2	4
Other debt securities
Debt securities AFS
Less than 12 months	1,535	1,790
12 months or longer	0	0
Total	1,535	1,790
Gross unrealized losses
Less than 12 months	1	1
12 months or longer	0	0
Total	$ 1	$ 1