INVESTMENTS - Fair Value of AFS Securities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair value
Less than 12 months	$ 62,098
Less than 12 months		$ 181,216
12 months or longer	118,258
12 months or longer		21,920
Total	180,356
Total		203,136
Gross unrealized losses
Less than 12 months	752
Less than 12 months		1,854
12 months or longer	2,468
12 months or longer		673
Total	3,220
Total		2,527
Mortgage-backed securities - U.S. agency-sponsored
Fair value
Less than 12 months	4,022
Less than 12 months		30,994
12 months or longer	13,143
12 months or longer		2,206
Total	17,165
Total		33,200
Gross unrealized losses
Less than 12 months	286
Less than 12 months		438
12 months or longer	439
12 months or longer		62
Total	725
Total		500
Mortgage-backed securities - Non-U.S. residential
Fair value
Less than 12 months	284
Less than 12 months		753
12 months or longer	2
12 months or longer		0
Total	286
Total		753
Gross unrealized losses
Less than 12 months	2
Less than 12 months		6
12 months or longer	0
12 months or longer		0
Total	2
Total		6
Mortgage-backed securities - Commercial
Fair value
Less than 12 months	79
Less than 12 months		150
12 months or longer	82
12 months or longer		57
Total	161
Total		207
Gross unrealized losses
Less than 12 months	1
Less than 12 months		1
12 months or longer	1
12 months or longer		1
Total	2
Total		2
Mortgage-backed securities
Fair value
Less than 12 months	4,385
Less than 12 months		31,897
12 months or longer	13,227
12 months or longer		2,263
Total	17,612
Total		34,160
Gross unrealized losses
Less than 12 months	289
Less than 12 months		445
12 months or longer	440
12 months or longer		63
Total	729
Total		508
U.S. Treasury
Fair value
Less than 12 months	8,389
Less than 12 months		79,050
12 months or longer	77,883
12 months or longer		7,404
Total	86,272
Total		86,454
Gross unrealized losses
Less than 12 months	42
Less than 12 months		856
12 months or longer	1,297
12 months or longer		115
Total	1,339
Total		971
Agency obligations
Fair value
Less than 12 months	277
Less than 12 months		8,857
12 months or longer	8,660
12 months or longer		1,163
Total	8,937
Total		10,020
Gross unrealized losses
Less than 12 months	2
Less than 12 months		110
12 months or longer	130
12 months or longer		14
Total	132
Total		124
U.S. Treasury and federal agency securities
Fair value
Less than 12 months	8,666
Less than 12 months		87,907
12 months or longer	86,543
12 months or longer		8,567
Total	95,209
Total		96,474
Gross unrealized losses
Less than 12 months	44
Less than 12 months		966
12 months or longer	1,427
12 months or longer		129
Total	1,471
Total		1,095
State and municipal securities
Fair value
Less than 12 months	1,614
Less than 12 months		1,009
12 months or longer	1,303
12 months or longer		1,155
Total	2,917
Total		2,164
Gross unrealized losses
Less than 12 months	34
Less than 12 months		11
12 months or longer	228
12 months or longer		234
Total	262
Total		245
Foreign government
Fair value
Less than 12 months	40,655
Less than 12 months		53,206
12 months or longer	15,053
12 months or longer		9,051
Total	55,708
Total		62,257
Gross unrealized losses
Less than 12 months	265
Less than 12 months		356
12 months or longer	331
12 months or longer		234
Total	596
Total		590
Corporate
Fair value
Less than 12 months	4,547
Less than 12 months		6,737
12 months or longer	2,077
12 months or longer		859
Total	6,624
Total		7,596
Gross unrealized losses
Less than 12 months	115
Less than 12 months		74
12 months or longer	42
12 months or longer		12
Total	157
Total		86
Asset-backed securities
Fair value
Less than 12 months	441
Less than 12 months		449
12 months or longer	55
12 months or longer		25
Total	496
Total		474
Gross unrealized losses
Less than 12 months	4
Less than 12 months		1
12 months or longer	0
12 months or longer		1
Total	4
Total		2
Other debt securities
Fair value
Less than 12 months	1,790
Less than 12 months		0
12 months or longer	0
12 months or longer		0
Total	1,790
Total		0
Gross unrealized losses
Less than 12 months	1
Less than 12 months		0
12 months or longer	0
12 months or longer		0
Total	$ 1
Total		0
Marketable equity securities AFS(3)
Fair value
Less than 12 months		11
12 months or longer		0
Total		11
Gross unrealized losses
Less than 12 months		1
12 months or longer		0
Total		$ 1