INVESTMENTS - Fair Value of AFS Securities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair value
Less than 12 months	$ 131,202	$ 122,278
12 months or longer	20,369	22,358
Total	151,571	144,636
Gross unrealized losses
Less than 12 months	982	1,394
12 months or longer	616	1,172
Total	1,598	2,566
Mortgage-backed securities - U.S. agency-sponsored
Fair value
Less than 12 months	24,545	23,534
12 months or longer	2,631	2,236
Total	27,176	25,770
Gross unrealized losses
Less than 12 months	275	436
12 months or longer	56	70
Total	331	506
Mortgage-backed securities - Prime
Fair value
Less than 12 months		1
12 months or longer		0
Total		1
Gross unrealized losses
Less than 12 months		0
12 months or longer		0
Total		0
Mortgage-backed securities - Non-U.S. residential
Fair value
Less than 12 months	1,267	486
12 months or longer	28	1,276
Total	1,295	1,762
Gross unrealized losses
Less than 12 months	8	0
12 months or longer	1	7
Total	9	7
Mortgage-backed securities - Commercial
Fair value
Less than 12 months	111	75
12 months or longer	42	58
Total	153	133
Gross unrealized losses
Less than 12 months	1	1
12 months or longer	1	0
Total	2	1
Mortgage-backed securities
Fair value
Less than 12 months	25,923	24,096
12 months or longer	2,701	3,570
Total	28,624	27,666
Gross unrealized losses
Less than 12 months	284	437
12 months or longer	58	77
Total	342	514
U.S. Treasury
Fair value
Less than 12 months	50,362	44,342
12 months or longer	4,392	1,335
Total	54,754	45,677
Gross unrealized losses
Less than 12 months	367	445
12 months or longer	41	7
Total	408	452
Agency obligations
Fair value
Less than 12 months	6,884	6,552
12 months or longer	1,231	250
Total	8,115	6,802
Gross unrealized losses
Less than 12 months	46	83
12 months or longer	19	2
Total	65	85
U.S. Treasury and federal agency securities
Fair value
Less than 12 months	57,246	50,894
12 months or longer	5,623	1,585
Total	62,869	52,479
Gross unrealized losses
Less than 12 months	413	528
12 months or longer	60	9
Total	473	537
State and municipal securities
Fair value
Less than 12 months	430	1,616
12 months or longer	1,669	3,116
Total	2,099	4,732
Gross unrealized losses
Less than 12 months	13	55
12 months or longer	278	702
Total	291	757
Foreign government
Fair value
Less than 12 months	40,112	38,226
12 months or longer	9,462	8,973
Total	49,574	47,199
Gross unrealized losses
Less than 12 months	202	243
12 months or longer	202	311
Total	404	554
Corporate
Fair value
Less than 12 months	6,330	7,011
12 months or longer	696	1,877
Total	7,026	8,888
Gross unrealized losses
Less than 12 months	65	129
12 months or longer	17	47
Total	82	176
Asset-backed securities
Fair value
Less than 12 months	1,148	411
12 months or longer	207	3,213
Total	1,355	3,624
Gross unrealized losses
Less than 12 months	3	0
12 months or longer	0	22
Total	3	22
Other
Fair value
Less than 12 months	0	5
12 months or longer	0	0
Total	0	5
Gross unrealized losses
Less than 12 months	0	0
12 months or longer	0	0
Total	0	0
Equity securities
Fair value
Less than 12 months	13	19
12 months or longer	11	24
Total	24	43
Gross unrealized losses
Less than 12 months	2	2
12 months or longer	1	4
Total	$ 3	$ 6