INVESTMENTS - Fair Value of AFS Debt Securities by Contractual Maturity Date (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair value
Total fair value	$ 295,573	$ 335,084
Mortgage-backed securities
Amoritzed cost
Amortized cost, due within 1 year	200	27
Amortized cost, after 1 but within 5 years	187	567
Amortized cost, after 5 but within 10 years	726	688
Amortized cost, after 10 years	35,410	42,171
Amortized cost	36,523	43,453
Fair value
Fair value, due within 1 year	200	27
Fair value, after 1 but within 5 years	188	571
Fair value, after 5 but within 10 years	776	757
Fair value, after 10 years	35,902	43,184
Total fair value	37,066	44,539
U.S. Treasury and federal agency securities
Amoritzed cost
Amortized cost, due within 1 year	27,539	34,834
Amortized cost, after 1 but within 5 years	94,520	108,160
Amortized cost, after 5 but within 10 years	432	1,150
Amortized cost, after 10 years	0	0
Amortized cost	122,491	144,144
Fair value
Fair value, due within 1 year	27,614	34,951
Fair value, after 1 but within 5 years	95,132	110,091
Fair value, after 5 but within 10 years	428	1,162
Fair value, after 10 years	0	0
Total fair value	123,174	146,204
State and municipal
Amoritzed cost
Amortized cost, due within 1 year	45	427
Amortized cost, after 1 but within 5 years	137	189
Amortized cost, after 5 but within 10 years	160	276
Amortized cost, after 10 years	2,368	2,861
Amortized cost	2,710	3,753
Fair value
Fair value, due within 1 year	45	428
Fair value, after 1 but within 5 years	140	198
Fair value, after 5 but within 10 years	168	267
Fair value, after 10 years	2,331	2,826
Total fair value	2,684	3,719
Foreign government
Amoritzed cost
Amortized cost, due within 1 year	47,441	48,133
Amortized cost, after 1 but within 5 years	65,523	67,365
Amortized cost, after 5 but within 10 years	5,560	5,908
Amortized cost, after 10 years	1,798	2,061
Amortized cost	120,322	123,467
Fair value
Fair value, due within 1 year	47,492	48,258
Fair value, after 1 but within 5 years	65,370	68,586
Fair value, after 5 but within 10 years	5,514	6,011
Fair value, after 10 years	1,818	2,113
Total fair value	120,194	124,968
All other
Amoritzed cost
Amortized cost, due within 1 year	6,108	6,661
Amortized cost, after 1 but within 5 years	5,434	7,814
Amortized cost, after 5 but within 10 years	853	1,018
Amortized cost, after 10 years	62	99
Amortized cost	12,457	15,592
Fair value
Fair value, due within 1 year	6,112	6,665
Fair value, after 1 but within 5 years	5,464	7,891
Fair value, after 5 but within 10 years	846	1,034
Fair value, after 10 years	33	64
Total fair value	$ 12,455	$ 15,654