INVESTMENTS - Fair Value of AFS Debt Securities by Contractual Maturity Date (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair value
Total fair value	$ 302,977	$ 335,084
Mortgage-backed securities
Amoritzed cost
Amortized cost, due within 1 year	107	27
Amortized cost, after 1 but within 5 years	315	567
Amortized cost, after 5 but within 10 years	679	688
Amortized cost, after 10 years	38,187	42,171
Amortized cost	39,288	43,453
Fair value
Fair value, due within 1 year	107	27
Fair value, after 1 but within 5 years	317	571
Fair value, after 5 but within 10 years	732	757
Fair value, after 10 years	38,601	43,184
Total fair value	39,757	44,539
U.S. Treasury and federal agency securities
Amoritzed cost
Amortized cost, due within 1 year	30,179	34,834
Amortized cost, after 1 but within 5 years	93,736	108,160
Amortized cost, after 5 but within 10 years	1,309	1,150
Amortized cost, after 10 years	0	0
Amortized cost	125,224	144,144
Fair value
Fair value, due within 1 year	30,264	34,951
Fair value, after 1 but within 5 years	94,589	110,091
Fair value, after 5 but within 10 years	1,294	1,162
Fair value, after 10 years	0	0
Total fair value	126,147	146,204
State and municipal
Amoritzed cost
Amortized cost, due within 1 year	379	427
Amortized cost, after 1 but within 5 years	92	189
Amortized cost, after 5 but within 10 years	245	276
Amortized cost, after 10 years	2,380	2,861
Amortized cost	3,096	3,753
Fair value
Fair value, due within 1 year	379	428
Fair value, after 1 but within 5 years	94	198
Fair value, after 5 but within 10 years	250	267
Fair value, after 10 years	2,356	2,826
Total fair value	3,079	3,719
Foreign government
Amoritzed cost
Amortized cost, due within 1 year	48,404	48,133
Amortized cost, after 1 but within 5 years	64,721	67,365
Amortized cost, after 5 but within 10 years	4,900	5,908
Amortized cost, after 10 years	2,097	2,061
Amortized cost	120,122	123,467
Fair value
Fair value, due within 1 year	48,458	48,258
Fair value, after 1 but within 5 years	64,846	68,586
Fair value, after 5 but within 10 years	4,803	6,011
Fair value, after 10 years	2,110	2,113
Total fair value	120,217	124,968
All other
Amoritzed cost
Amortized cost, due within 1 year	6,436	6,661
Amortized cost, after 1 but within 5 years	6,200	7,814
Amortized cost, after 5 but within 10 years	1,078	1,018
Amortized cost, after 10 years	60	99
Amortized cost	13,774	15,592
Fair value
Fair value, due within 1 year	6,435	6,665
Fair value, after 1 but within 5 years	6,234	7,891
Fair value, after 5 but within 10 years	1,080	1,034
Fair value, after 10 years	28	64
Total fair value	$ 13,777	$ 15,654