INVESTMENTS - Fair Value of AFS Securities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair value
Less than 12 months	$ 109,566
Less than 12 months		$ 181,216
12 months or longer	106,356
12 months or longer		21,920
Total	215,922
Total		203,136
Gross unrealized losses
Less than 12 months	1,502
Less than 12 months		1,854
12 months or longer	3,406
12 months or longer		673
Total	4,908
Total		2,527
Mortgage-backed securities - U.S. agency-sponsored
Fair value
Less than 12 months	21,723
Less than 12 months		30,994
12 months or longer	18,828
12 months or longer		2,206
Total	40,551
Total		33,200
Gross unrealized losses
Less than 12 months	574
Less than 12 months		438
12 months or longer	1,001
12 months or longer		62
Total	1,575
Total		500
Mortgage-backed securities - Non-U.S. residential
Fair value
Less than 12 months	256
Less than 12 months		753
12 months or longer	1
12 months or longer		0
Total	257
Total		753
Gross unrealized losses
Less than 12 months	1
Less than 12 months		6
12 months or longer	0
12 months or longer		0
Total	1
Total		6
Mortgage-backed securities - Commercial
Fair value
Less than 12 months	168
Less than 12 months		150
12 months or longer	51
12 months or longer		57
Total	219
Total		207
Gross unrealized losses
Less than 12 months	2
Less than 12 months		1
12 months or longer	1
12 months or longer		1
Total	3
Total		2
Mortgage-backed securities
Fair value
Less than 12 months	22,147
Less than 12 months		31,897
12 months or longer	18,880
12 months or longer		2,263
Total	41,027
Total		34,160
Gross unrealized losses
Less than 12 months	577
Less than 12 months		445
12 months or longer	1,002
12 months or longer		63
Total	1,579
Total		508
U.S. Treasury
Fair value
Less than 12 months	27,095
Less than 12 months		79,050
12 months or longer	65,789
12 months or longer		7,404
Total	92,884
Total		86,454
Gross unrealized losses
Less than 12 months	279
Less than 12 months		856
12 months or longer	1,670
12 months or longer		115
Total	1,949
Total		971
Agency obligations
Fair value
Less than 12 months	1,549
Less than 12 months		8,857
12 months or longer	8,004
12 months or longer		1,163
Total	9,553
Total		10,020
Gross unrealized losses
Less than 12 months	15
Less than 12 months		110
12 months or longer	182
12 months or longer		14
Total	197
Total		124
U.S. Treasury and federal agency securities
Fair value
Less than 12 months	28,644
Less than 12 months		87,907
12 months or longer	73,793
12 months or longer		8,567
Total	102,437
Total		96,474
Gross unrealized losses
Less than 12 months	294
Less than 12 months		966
12 months or longer	1,852
12 months or longer		129
Total	2,146
Total		1,095
State and municipal securities
Fair value
Less than 12 months	1,811
Less than 12 months		1,009
12 months or longer	1,260
12 months or longer		1,155
Total	3,071
Total		2,164
Gross unrealized losses
Less than 12 months	48
Less than 12 months		11
12 months or longer	221
12 months or longer		234
Total	269
Total		245
Foreign government
Fair value
Less than 12 months	48,491
Less than 12 months		53,206
12 months or longer	11,598
12 months or longer		9,051
Total	60,089
Total		62,257
Gross unrealized losses
Less than 12 months	463
Less than 12 months		356
12 months or longer	306
12 months or longer		234
Total	769
Total		590
Corporate
Fair value
Less than 12 months	6,556
Less than 12 months		6,737
12 months or longer	798
12 months or longer		859
Total	7,354
Total		7,596
Gross unrealized losses
Less than 12 months	114
Less than 12 months		74
12 months or longer	25
12 months or longer		12
Total	139
Total		86
Asset-backed securities
Fair value
Less than 12 months	604
Less than 12 months		449
12 months or longer	27
12 months or longer		25
Total	631
Total		474
Gross unrealized losses
Less than 12 months	6
Less than 12 months		1
12 months or longer	0
12 months or longer		1
Total	6
Total		2
Other debt securities
Fair value
Less than 12 months	1,313
Less than 12 months		0
12 months or longer	0
12 months or longer		0
Total	1,313
Total		0
Gross unrealized losses
Less than 12 months	0
Less than 12 months		0
12 months or longer	0
12 months or longer		0
Total	$ 0
Total		0
Equity securities
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